Hi,
It has happened to me several times since updating from 4.2.4 to 4.2.6 that the settings window of a virtual machine appears blank or corrupted, e.g. showing only the toolbar, and no ok or cancel buttons. It requires to force quite the VirtualBox application. The problem apparently occurs regardless which virtual machine is selected or the machine state. However I have not been able to determine what triggers this problem. There is nothing in the log for the VirtualBox application or VM, at least nothing anywhere near the time the issue occurs.
I also noticed that starting with 4.2.4, opening any VM settings takes an unusual 7 seconds.
I created a new ticket: https://www.virtualbox.org/ticket/11429
Mac Pro 4.1, 10.6.8
Kind regards.