Sometimes calls in Qm seem to go on forever... even if they have been terminated. This is often the case when your users exit the key by pressing a numeric key; some versions of Asterisk don't log this event correctly, so the call appears to be going on and on.

In order to check if this is the case, you should monitor your queue_log file when you exit a call by pressing a key; you should expect a line that looks like:
1106553723|1106553678.2598|queue-f|NONE|EXITWITHKEY|3|1
If such a line is not present, you may detect the event via the ${QUEUESTATUS} variable when the queue() app terminates, and produce a record like the following one:
exten => s,1,System( echo "${EPOCH}|${UNIQUEID}|myqueue|NONE|EXITWITHKEY|key|1|" >> /var/log/asterisk/queue_log )
Where "myqueue" is the queue name and "key" is the key pressed (if you need to track it, otherwise set it to 1).

See also Handling ghost calls.