Ringback after hangup

I have just upgraded from 2.0.1 to the new 2.1.0

Since then I have a small problem.
I have been testing by calling my regular POTS line.
When I do this it all works fine. Then I end the call.
Within about 10 seconds, after both phones (VoIP and POTS) have been hung up, the POTS line rings again. When I pick up the handset, it is silent. I can then hangup and all is good again.

Thi happens on every single call to the POTS number. It did not occur in the previous version.

Any hints on what I should be looking for, or has anyone else had the same issue?