No hung up signal while injected sound file is playing (MeetMe)


I have Asterisk 11.20.0 running on CentOS 6.7.
The server is managing phone calls between two persons where while an active call a sound file can be injected per MeetMe into the conference so that both persons can hear that sound file. When the callee person hang up while such an injected sound file is NOT currently in playback, a hung up signal can be detected. But if the callee hang up while the injected sound file is in playback a hung up signal is not detected. I am trying since 8 hours to find the reason for this issue but I failed. Okay, I give in I am far away from being an Asterisk expert…

Here are the regarding extension entrys:

exten => s,1,NoOp(${CONF})
exten => s,n,NoOp(INIT_CHANNEL: ${CDR(channel)})
exten => s,n,Set(SHARED(INIT_CHANNEL,${CDR(dstchannel)})=${CDR(channel)})
exten => s,n,Set(SHARED(CONF,${CDR(dstchannel)})=${CONF})
exten => s,n,MeetMe(${CONF},Akmqd)
exten => s,n,Hangup

exten => s,1,NoOp(${SHARED(CONF)})
exten => s,n,Wait(0.5)
exten => s,n,NoOp(${SHARED(INIT_CHANNEL)})
exten => s,n,MeetMe(${SHARED(CONF)},kxqd)
exten => s,n,AGI(,${SHARED(INIT_CHANNEL)})
exten => s,n,NoOp(“NOT_IN_THE_MEETME”)
exten => s,n,Hangup

exten => s,1,MeetMe(${CONF},qd)
exten => s,n,NoOp(“AFTER MEETME”)

I know the more informations the better but I have no idea which settings from which config files may be important for solving my problem. Please let me know if and what more informations I should post.

Thank you,