Paging Problem

I have about 100 SNOM phones connected to FreePBX and we have paging group that include almost all our phones.
We use paging not too often and it used to work, but since then we did many upgrades and I’m not sure when the paging started to make problems.

When a user (lets say X) calls the paging group he makes an announcement and all the phones hear it normally. The problem is that when this user X hang up his phone all the other phones show that they still have an active call with this user X (they don’t get disconnected)

Any idea what it can be ? How can I make them disconnect ?