Trouble with ROS on VirtualBox (OS X host)

I'm having trouble running Reactos 0.3.11 on VirtualBox (on an OSX host).

The splash screen is fine, but when the desktop appears the colours go
all crazy.  Looks like this happens when some kind of background/desktop
image is being displayed.

Also, when the mouse is moved over icons (e.g. MyComputer), the icons
get smudged.

I have tried using VB 3.1.6, 3.18 and 3.2.0 but they all do the same thing.

Anyone else seen similar issues ??

I did have it working once (on VB 3.1.6 I think) for a short while, but
as soon as I installed the guest additions things when belly up.

So, any tips or hints on how to get ROS working smoothly on VirtualBox ??

Are there any settings that I should definitely set or unset ??

Thanks, Brendan.