diff -d -u -r1.1.1.3 chan_sip.c
--- channels/chan_sip.c	23 Apr 2008 14:24:27 -0000	1.1.1.3
+++ channels/chan_sip.c	18 Nov 2008 16:28:30 -0000
@@ -795,6 +796,7 @@
 #define SIP_PAGE2_RFC2833_COMPENSATE    (1 << 25)	/*!< 25: ???? */
 #define SIP_PAGE2_BUGGY_MWI		(1 << 26)	/*!< 26: Buggy CISCO MWI fix */
 #define SIP_PAGE2_OUTGOING_CALL         (1 << 27)       /*!< 27: Is this an outgoing call? */
+#define SIP_PAGE2_GOT_OK_FOR_INVITE     (1 << 31)       /*!< 31: Got OK for INVITE? */
 
 #define SIP_PAGE2_FLAGS_TO_COPY \
 	(SIP_PAGE2_ALLOWSUBSCRIBE | SIP_PAGE2_ALLOWOVERLAP | SIP_PAGE2_VIDEOSUPPORT | \
@@ -12266,6 +12306,7 @@
 		}
 
 		if (!ast_test_flag(req, SIP_PKT_IGNORE) && p->owner) {
+			ast_set_flag(&p->flags[1], SIP_PAGE2_GOT_OK_FOR_INVITE);	
 			if (!reinvite) {
 				ast_queue_control(p->owner, AST_CONTROL_ANSWER);
 			} else {	/* RE-invite */
@@ -13763,6 +13805,20 @@
 
 	/* Check if this is a loop */
 	if (ast_test_flag(&p->flags[0], SIP_OUTGOING) && p->owner && (p->owner->_state != AST_STATE_UP)) {
+		/* Loop mis-detection prevention hack: Is this a re-INVITE that came too early for us,
+		* i.e., after we got the OK but before the dialing thread read the ANSWER control
+		* frame? If this situation is detected, we fake that the re-INVITE request packet was
+		* never received and hope that the channel is UP when the packet is retransmitted by
+		* the other side. WARNING: it is untested what happens if the other side does not
+		* retransmit the request.
+		*/
+		if (ast_test_flag(&p->flags[1], SIP_PAGE2_GOT_OK_FOR_INVITE)) {
+			ast_log(LOG_WARNING, "Ignoring re-INVITE on %s to prevent loop mis-detection (got OK but channel is not UP yet).\n", p->owner->name);
+			/* Do not send anything back but decrement the incoming sequence counter,
+			 * otherweise the retransmitted re-INVITE will be ignored. */
+			--p->icseq;
+			return 0;
+		}
 		/* This is a call to ourself.  Send ourselves an error code and stop
 	   	processing immediately, as SIP really has no good mechanism for
 	   	being able to call yourself */