I have an installation or two that has these odd calls. They are using Asterisk 11, Fpbz 6.12 and 13. The complaint was that they were having calls wheree 1/2 of the audio was lost for up to 10 seconds. I ran tcpdump and caught a call that was outgoing, and also had an incoming call within it. Wireshark shows that there was an incoming call and an outgoing call at the same time. We can hear the inside audio of the outgoing call and both sides of the incoming call. None of the parties appear to hear the erant audio. I upgrded one of the installations to Asterisk 13 last night. I can provide the pcap file if anyone wants to look at it.