Installed Ubuntu 12.04 LTS 64bit on Virtualbox 4.3.6 (latest version) and Zimbra Collaboration suite under Windows Server 2012

The VM screen after some time of inactivity flickers if I activate the VM with my mouse. All I can do is shutdown. It does not seem to affect Ubuntu/Zimbra functionality.

This only happens after I install Zimbra. I've created a number of Ubuntu VM's in the last week (testing installation of Zimbra) and it only starts after installation

Anyone else run into this?