VirtualBox breaking Unity's Compiz Scale Plugin

[shockwave]

My setup: Ubuntu 16.04 host, Win8 64bit guest.

On the host when I enable the Compiz Scale plugin in CompizConfig Settings Manager and give it a window binding (say the top of the screen initiates the plugin) everything works except when Virtualbox is the active window. When Virtualbox is the active window it "steals" the mouse movement when moving to the top of the screen and leaves the desktop in a bad state. The scale plugin is now broken (it no longer triggers) until I manually switch to a different active application then re-initiate the scale plugin via the mouse at the top of the screen. After that it works fine again until I try to trigger it with VirtualBox being the active window. If, however, I press the host key (right ctrl in my case) before I move the cursor to the top of the screen it initiates the Scale plugin as expected.

On previous versions of VirtualBox this all worked. Not exactly sure what version this started happening in unfortunately.

This is quite hard to explain, but it is 100% reproducible on my machine. I've tried everything from clearing all gnome settings, clearing all compiz settings, etc.

Let me know if you need any more information.