[Asterisk-Users] asterisk not detecting call hangup

[snacktime]

I'm not sure whether this is an issue with my provider or if it's just
an iax issue.  I have a DID coming into my asterisk box via iax.  When
I call it from a pots line and hangup, my asterisk box doesn't detect
the hangup until the call reaches voicemail at which time I get the
following message:

app.c:619 ast_play_and_record: No audio available

What would be the most likely root of the problem?  I've never seen
this on DID's that were terminated to my * box via SIP.  Is this an
IAX issue?

Chris