virtualbox.org

System:

VB version 4.3.20 r96996

Host:
- 2013 iMac 27 OSX 10.10.2 24G RAM 3.5GHz i7 NVIDA GeForce GTX 775M 2048MB
- dual monitors ( driving another iMac 27 as a display )

Guest:
- Win 8.1 installed from disk, updated to latest fixes as of 2/1/2015
- Guest additions installed

I can switch between display modes, but in seamless mode I can still see the guest background, and if I put a MAC window on top of it and click on the guest, the Mac window will dissapear behind it. Weird thing is, if I change the guest ( win 8.1 ) background to anything different while running the guest, suddenly seamless mode starts working. It works until I shut down the guest and re-start it. Then I have to yet again change the background to get it to start working again. It does not seem to matter what I change it to, as long as I change it.

Also, when seamless mode is "working", I cannot click the start button and see what that menu says, I have to change back to scaled or full screen mode to be able to, for example, restart the guest, since I cannot see the pop up menu.

BTW, this is probably not relevant, but I have been using XP as a guest for a few years now, and have never had any issues with seamless mode. It is only since I tried Win 8.1 that I have had problems.

A few more things:
- guest display is set for max memory ( 256MB )
- 2D and 3D acceleration turned on ( but likely not needed )
- Guest OS is win 8.1 32 bit, not 64 bit ( I need to run some old 32 bit apps ). So, it is set for max 32 bit addressable RAM : 4GB ( which is plenty for my needs ).

@mrggg I'm experiencing the same kind of problems.

I'm using:
host Ubuntu 14.10
Guest Windows 8.1 64 bits
VirtualBox 4.3.10/Guest Add. 4.3.10.

The trick of changing the guest wallpaper worked fine, but still a pain to do every time the system boots...