Lync Client Freezes on Windows 8 Release Preview

I have been using Windows 8 Release Preview and have an issue with Lync Client (4.0.7577)

Everything appears to work fine until I make an audio call using Enterprise Voice. The call connects fine but I cannot hang up.

When I try to hang up the client freezes and becomes unresponsive. Only solution is to force quit the application.

I have tried reinstalling Windows 8 but same behaviour remains, so it appears that its a Windows 8 issue with the Lync client.

I have enabled Logging to the Event Viewer but nothing there.

Any ideas?

Thanks

Alan