; extensions.conf:
[conf]
exten => s,1,Progress()
	same => n,MSet(CONFBRIDGE(bridge,template)=silentbridge,CONFBRIDGE(user,template)=incogtalkeroptimized)
	same => n,MSet(CONFBRIDGE(user,wait_marked)=yes,CONFBRIDGE(user,end_marked)=yes,CONFBRIDGE(user,dtmf_passthrough)=no,CONFBRIDGE(user,dsp_drop_silence)=yes)
	same => n,Set(join=silence/2)
	same => n,Set(leave=silence/2)
		same => n,Set(CONFBRIDGE(user,quiet)=no)
		same => n,Set(CONFBRIDGE(bridge,sound_join)=${IF(${EXISTS(${join})}?${join}:silence/1)})
		same => n,Set(CONFBRIDGE(bridge,sound_leave)=${IF(${EXISTS(${join})}?${leave}:silence/1)})
		same => n,Set(CONFBRIDGE(bridge,sound_kicked)=silence/1)
		same => n,Set(CONFBRIDGE(bridge,sound_wait_for_leader)=silence/3)
	same => n,Originate(Local/123@conf-announce,exten,conf-announcement,${ARG1},1,,a)
	
	same => n,Wait(0.8) ; this is to force the bug to manifest, to make the call SUCCEED, comment this out.
	
	same => n,ConfBridge(interceptdrum123)
	same => n,Hangup()

[conf-announcement]
exten => _[0-9A-Za-z].,1,Originate(Local/${EXTEN}@conf-spy,app,Wait,10)
	same => n,Playback(silence/9)
	same => n,Hangup()

[conf-announce]
exten => _[0-9A-Za-z].,1,Answer()
	same => n,ConfBridge(interceptdrum123,silentbridge,incogtalkeroptimized)
	same => n,Hangup()

[conf-monitor]
exten => _[0-9A-Za-z].,1,Answer()
	same => n,ConfBridge(interceptdrum123,silentbridge,incogtalkeroptimized)
	same => n,Hangup()

[conf-spy]
exten => _[0-9A-Za-z].,1,Set(CDR_PROP(disable)=1)
	same => n,Answer()
	same => n,ConfBridge(interceptdrum123,silentbridge,incogtalkeroptimized)
	same => n,Hangup()

; confbridge.conf:
;[silentbridge]
;type=bridge
;sound_join=/var/lib/asterisk/sounds/en/silence/1
;sound_leave=/var/lib/asterisk/sounds/en/silence/1

;[incogtalker]
;type=user
;dsp_drop_silence=no
;quiet=yes
;dtmf_passthrough=yes
;answer_channel=no

;[incogtalkeroptimized]
;type=user
;dsp_drop_silence=no
;quiet=yes
;dtmf_passthrough=yes
;answer_channel=no


BAD call (with bug):

pbxdev*CLI> core set debug 0
Core debug was 1 and is now OFF.
pbxdev*CLI> channel originate Local/s@conf application Wait 10
[Jan 30 18:17:12]     -- Called s@conf
[Jan 30 18:17:12]     -- Executing [s@conf:1] Progress("Local/s@conf-00000077;2", "") in new stack
[Jan 30 18:17:12]     -- Local/s@conf-00000077;1 is making progress
[Jan 30 18:17:12]     -- Executing [s@conf:2] MSet("Local/s@conf-00000077;2", "CONFBRIDGE(bridge,template)=silentbridge,CONFBRIDGE(user,template)=incogtalkeroptimized") in new stack
[Jan 30 18:17:12]     -- Executing [s@conf:3] MSet("Local/s@conf-00000077;2", "CONFBRIDGE(user,wait_marked)=yes,CONFBRIDGE(user,end_marked)=yes,CONFBRIDGE(user,dtmf_passthrough)=no,CONFBRIDGE(user,dsp_drop_silence)=yes") in new stack
[Jan 30 18:17:12]     -- Executing [s@conf:4] Set("Local/s@conf-00000077;2", "join=silence/2") in new stack
[Jan 30 18:17:12]     -- Executing [s@conf:5] Set("Local/s@conf-00000077;2", "leave=silence/2") in new stack
[Jan 30 18:17:12]     -- Executing [s@conf:6] Set("Local/s@conf-00000077;2", "CONFBRIDGE(user,quiet)=no") in new stack
[Jan 30 18:17:12]     -- Executing [s@conf:7] Set("Local/s@conf-00000077;2", "CONFBRIDGE(bridge,sound_join)=silence/2") in new stack
[Jan 30 18:17:12]     -- Executing [s@conf:8] Set("Local/s@conf-00000077;2", "CONFBRIDGE(bridge,sound_leave)=silence/2") in new stack
[Jan 30 18:17:12]     -- Executing [s@conf:9] Set("Local/s@conf-00000077;2", "CONFBRIDGE(bridge,sound_kicked)=silence/1") in new stack
[Jan 30 18:17:12]     -- Executing [s@conf:10] Set("Local/s@conf-00000077;2", "CONFBRIDGE(bridge,sound_wait_for_leader)=silence/3") in new stack
[Jan 30 18:17:12]     -- Executing [s@conf:11] Originate("Local/s@conf-00000077;2", "Local/123@conf-announce,exten,conf-announcement,,1") in new stack
[Jan 30 18:17:12]     -- Called 123@conf-announce
[Jan 30 18:17:12]     -- Executing [123@conf-announce:1] Answer("Local/123@conf-announce-00000078;2", "") in new stack
[Jan 30 18:17:12]     -- Local/123@conf-announce-00000078;1 answered
[Jan 30 18:17:12]     -- Executing [123@conf-announcement:1] Originate("Local/123@conf-announce-00000078;1", "Local/123@conf-spy,app,Wait,10") in new stack
[Jan 30 18:17:12]     -- Called 123@conf-spy
[Jan 30 18:17:12]     -- Executing [123@conf-spy:1] Set("Local/123@conf-spy-00000079;2", "CDR_PROP(disable)=1") in new stack
[Jan 30 18:17:12]     -- Executing [123@conf-spy:2] Answer("Local/123@conf-spy-00000079;2", "") in new stack
[Jan 30 18:17:12]     -- Local/123@conf-spy-00000079;1 answered
[Jan 30 18:17:12]     -- Executing [s@conf:12] Wait("Local/s@conf-00000077;2", "0.8") in new stack
[Jan 30 18:17:12]     -- Executing [123@conf-announcement:2] Playback("Local/123@conf-announce-00000078;1", "silence/9") in new stack
[Jan 30 18:17:12]     -- <Local/123@conf-announce-00000078;1> Playing 'silence/9.ulaw' (language 'en')
[Jan 30 18:17:12]     -- Executing [123@conf-announce:2] ConfBridge("Local/123@conf-announce-00000078;2", "interceptdrum123,silentbridge,incogtalkeroptimized") in new stack
[Jan 30 18:17:12]     -- Channel CBAnn/interceptdrum123-0000007a;2 joined 'softmix' base-bridge <451803c7-d1aa-42a8-98c7-30250ec0e2c0>
[Jan 30 18:17:12]     -- Channel Local/123@conf-announce-00000078;2 joined 'softmix' base-bridge <451803c7-d1aa-42a8-98c7-30250ec0e2c0>
[Jan 30 18:17:13]     -- Executing [123@conf-spy:3] ConfBridge("Local/123@conf-spy-00000079;2", "interceptdrum123,silentbridge,incogtalkeroptimized") in new stack <---------------- another channel joins the bridge first
[Jan 30 18:17:13]     -- Channel Local/123@conf-spy-00000079;2 joined 'softmix' base-bridge <451803c7-d1aa-42a8-98c7-30250ec0e2c0>
[Jan 30 18:17:13]     -- Executing [s@conf:13] ConfBridge("Local/s@conf-00000077;2", "interceptdrum123") in new stack <------------------------ we join the bridge second.
[Jan 30 18:17:13]     -- <Local/s@conf-00000077;2> Playing 'conf-waitforleader.ulaw' (language 'en') <----------------------------------------------- THIS SHOULD NOT PLAY!!!!!!!!!
[Jan 30 18:17:16]     -- Channel Local/s@conf-00000077;2 joined 'softmix' base-bridge <451803c7-d1aa-42a8-98c7-30250ec0e2c0>
[Jan 30 18:17:16]     -- <CBAnn/interceptdrum123-0000007a;1> Playing '/var/lib/asterisk/sounds/en/silence/1.ulaw' (language 'en')
pbxdev*CLI>
Disconnected from Asterisk server




Now, suppose I tweak some things to guarantee that the original channel joins the confbridge first.
Issue goes away:

GOOD call (no bug):

pbxdev*CLI> channel originate Local/s@conf application Wait 10
[Jan 30 18:19:24]     -- Called s@conf
[Jan 30 18:19:24]     -- Executing [s@conf:1] Progress("Local/s@conf-00000083;2", "") in new stack
[Jan 30 18:19:24]     -- Local/s@conf-00000083;1 is making progress
[Jan 30 18:19:24]     -- Executing [s@conf:2] MSet("Local/s@conf-00000083;2", "CONFBRIDGE(bridge,template)=silentbridge,CONFBRIDGE(user,template)=incogtalkeroptimized") in new stack
[Jan 30 18:19:24]     -- Executing [s@conf:3] MSet("Local/s@conf-00000083;2", "CONFBRIDGE(user,wait_marked)=yes,CONFBRIDGE(user,end_marked)=yes,CONFBRIDGE(user,dtmf_passthrough)=no,CONFBRIDGE(user,dsp_drop_silence)=yes") in new stack
[Jan 30 18:19:24]     -- Executing [s@conf:4] Set("Local/s@conf-00000083;2", "join=silence/2") in new stack
[Jan 30 18:19:24]     -- Executing [s@conf:5] Set("Local/s@conf-00000083;2", "leave=silence/2") in new stack
[Jan 30 18:19:24]     -- Executing [s@conf:6] Set("Local/s@conf-00000083;2", "CONFBRIDGE(user,quiet)=no") in new stack
[Jan 30 18:19:24]     -- Executing [s@conf:7] Set("Local/s@conf-00000083;2", "CONFBRIDGE(bridge,sound_join)=silence/2") in new stack
[Jan 30 18:19:24]     -- Executing [s@conf:8] Set("Local/s@conf-00000083;2", "CONFBRIDGE(bridge,sound_leave)=silence/2") in new stack
[Jan 30 18:19:24]     -- Executing [s@conf:9] Set("Local/s@conf-00000083;2", "CONFBRIDGE(bridge,sound_kicked)=silence/1") in new stack
[Jan 30 18:19:24]     -- Executing [s@conf:10] Set("Local/s@conf-00000083;2", "CONFBRIDGE(bridge,sound_wait_for_leader)=silence/3") in new stack
[Jan 30 18:19:24]     -- Executing [s@conf:11] Originate("Local/s@conf-00000083;2", "Local/123@conf-announce,exten,conf-announcement,,1,,a") in new stack
[Jan 30 18:19:24]     -- Executing [s@conf:12] Wait("Local/s@conf-00000083;2", "0.01") in new stack
[Jan 30 18:19:24]     -- Called 123@conf-announce
[Jan 30 18:19:24]     -- Executing [123@conf-announce:1] Answer("Local/123@conf-announce-00000084;2", "") in new stack
[Jan 30 18:19:24]     -- Local/123@conf-announce-00000084;1 answered
[Jan 30 18:19:24]     -- Executing [123@conf-announcement:1] Originate("Local/123@conf-announce-00000084;1", "Local/123@conf-spy,app,Wait,10") in new stack
[Jan 30 18:19:24]     -- Called 123@conf-spy
[Jan 30 18:19:24]     -- Executing [123@conf-spy:1] Set("Local/123@conf-spy-00000085;2", "CDR_PROP(disable)=1") in new stack
[Jan 30 18:19:24]     -- Executing [123@conf-spy:2] Answer("Local/123@conf-spy-00000085;2", "") in new stack
[Jan 30 18:19:24]     -- Local/123@conf-spy-00000085;1 answered
[Jan 30 18:19:24]     -- Executing [123@conf-announcement:2] Playback("Local/123@conf-announce-00000084;1", "silence/9") in new stack
[Jan 30 18:19:24]     -- <Local/123@conf-announce-00000084;1> Playing 'silence/9.ulaw' (language 'en')
[Jan 30 18:19:24]     -- Executing [123@conf-announce:2] Wait("Local/123@conf-announce-00000084;2", "1") in new stack
[Jan 30 18:19:24]     -- Executing [s@conf:13] ConfBridge("Local/s@conf-00000083;2", "interceptdrum123") in new stack <-------------------------- we join the bridge first
[Jan 30 18:19:24]     -- Channel CBAnn/interceptdrum123-00000086;2 joined 'softmix' base-bridge <60c763b2-2d48-49a5-a3c6-8d3f5a0fcffe>
[Jan 30 18:19:24]     -- <Local/s@conf-00000083;2> Playing 'silence/3.ulaw' (language 'en') <-------------------------------- the specified file is correctly played
[Jan 30 18:19:24]     -- Executing [123@conf-spy:3] ConfBridge("Local/123@conf-spy-00000085;2", "interceptdrum123,silentbridge,incogtalkeroptimized") in new stack <------------------------- then another channel joins
[Jan 30 18:19:24]     -- Channel Local/123@conf-spy-00000085;2 joined 'softmix' base-bridge <60c763b2-2d48-49a5-a3c6-8d3f5a0fcffe>
[Jan 30 18:19:25]     -- Executing [123@conf-announce:3] ConfBridge("Local/123@conf-announce-00000084;2", "interceptdrum123,silentbridge,incogtalkeroptimized") in new stack
[Jan 30 18:19:25]     -- Channel Local/123@conf-announce-00000084;2 joined 'softmix' base-bridge <60c763b2-2d48-49a5-a3c6-8d3f5a0fcffe>
[Jan 30 18:19:27]     -- Channel Local/s@conf-00000083;2 joined 'softmix' base-bridge <60c763b2-2d48-49a5-a3c6-8d3f5a0fcffe>
[Jan 30 18:19:27]     -- <CBAnn/interceptdrum123-00000086;1> Playing 'silence/2.ulaw' (language 'en')
[Jan 30 18:19:33]     -- Executing [123@conf-announcement:3] Hangup("Local/123@conf-announce-00000084;1", "") in new stack
[Jan 30 18:19:33]   == Spawn extension (conf-announcement, 123, 3) exited non-zero on 'Local/123@conf-announce-00000084;1'
[Jan 30 18:19:33]     -- Channel Local/123@conf-announce-00000084;2 left 'softmix' base-bridge <60c763b2-2d48-49a5-a3c6-8d3f5a0fcffe>