User logs out of phone, but stays logged in queue

When using restful apps on aastra/Mitel 57i
A user can log into a queue through the queue agent app.
A user can log out of the phone with the end point manager app.
Looking at active queue members, the user is still active in the queue, yet no phone is registered to the user. This has lead to queues with no agents getting clogged with disgruntled customers.