Strange asterisk behaviour?

after i registered both voip phones at asterisk i start a call.

asterisk ends the session after the ACK directly with “bye” to the callee, but sends ok to the caller. i don’t understand why?

phone ------------ asterisk-------------- phone

… <----trying
… invite---->

… bye---->
… <—ok
ack ---->
…<----ok (response bye)
bye ---->
… <----ok
…request bye ---->

here the other phone doesn’t respond anymore because it has allready closed the session due to the previous bye request.

why does asterisk send the bye after the ACK?

is it a bug?

best regards george

it looks as if the callee-sdp is the cause …
but asterisk doesn’t report an mistake