IVR Hangup Issue

I have been using FXO for a while now with a simple inbound route to Ring Group.

I now want to introduce an IVR.

The problem is that if the caller hangs up after Key Press then the FXO trunk does not drop.

I have tested and can confirm:
- Inbound to Ring Group = Hangup disconnects trunk
- Inbound to IVR, caller hangs up during Voice Prompt = Hangup disconnects trunk
- Inbound to IVR, caller Key Press. caller hangs up = Trunk stays in use.

I have tweaked the hangup detection settings but unable to get it to drop. Plus as it works when Inbound is to Ring Group I’m questioning is that is the problem?

Any help greatly received.