asterisk users - Oct 2016 - queue show - extensions in call going from (in use) to (not in use)

Running Asterisk 11.23.0 realtime currently, I've noticed some odd queue
behavior only starting today. We are using queues in conjunction with FOP2 to
show agent status, etc.  As of today, we noticed that an agent will be on a call
but show as available.

On an inbound queue call, when an agent answers the output of `queue show` will
look like this:

3103 (Local/AG-000-NF-1174 at fromotherpbx/n from Custom:3103-tenant) (ringinuse
disabled) (realtime) (in call) (In use) has taken 1 calls (last was 69 secs ago)

Sometimes, and not always, the call will turn into this, causing FOP to show the
agent as available again:

3103 (Local/AG-000-NF-1174 at fromotherpbx/n from Custom:3103-tenant) (ringinuse
disabled) (realtime) (in call) (Not in use) has taken 1 calls (last was 282 secs
ago)

Out of curiosity, is there something that would make the queue app think that
the extension is no longer in use?  My thought process would be that if the
agent is in a call, that it should always be 'in use', but perhaps
I'm missing some pertinent information here.

Any tips would be appreciated.

Thanks,
Derek B.

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