This seems to be related to some sort of CANCEL message, possibly from Freeswitch, but I don't have the message buffer handy and the issue is not easily reproducible.
Any ideas?
(gdb) where #0 0x00002b1a751554c8 in build_local_reparse (Trans=<value optimized out>, branch=<value optimized out>, len=0x7fff2944e4dc, method=0x2b1a75173bc8 "CANCEL", method_len=6, to=0x2b1a790a0f48, reason=0x7fff2944e568) at t_msgbuilder.c:476 #1 0x00002b1a7512411e in cancel_branch (t=0x2b1a78f2aecb, branch=0, reason=0x7fff2944e568, flags=0) at t_cancel.c:285 #2 0x00002b1a7513c361 in fake_reply (ticks=<value optimized out>, tl=<value optimized out>, p=<value optimized out>) at timer.c:320 #3 final_response_handler (ticks=<value optimized out>, tl=<value optimized out>, p=<value optimized out>) at timer.c:489 #4 retr_buf_handler (ticks=<value optimized out>, tl=<value optimized out>, p=<value optimized out>) at timer.c:546 #5 0x000000000051b55a in timer_list_expire () at timer.c:894 #6 timer_handler () at timer.c:957 #7 timer_main () at timer.c:996 #8 0x0000000000469fb4 in main_loop () at main.c:1618 #9 0x000000000046be9f in main (argc=<value optimized out>, argv=0x7fff2944e898) at main.c:2398