I haven't been able to reproduce this particular issue after numerous restarts, but a new one appears to have popped up. The keyboard has really been acting strange since the update. Sometimes certain hotkeys are randomly triggered (e.g. WinKey+E to open Windows Explorer). I've even had the WinKey+TAB combination trigger Windows' Aero Task switcher, even though I have Command mapped to the WinKey (which is a default mapping), and Command + TAB should instead launch OS X's task switcher. Disabling Copy & Paste in the VM's settings seems to have fixed it for the time being.