switching to VBoxVideo.sys from VBEMP and rebooting once introduces icon transparency issues (at least until another reboot)

0.4.9-RC-23-g519cdd3 gcc dbg
VBox 4.3.40 with installed additions graphics driver: VBoxVideo.sys
32bit colour depth selected

When using VBoxVideo.sys from guest additions instead VBEMP, we see more icons having transparency issues.
e.g: the Firefox 28 desktop icon and our folder icons within explorer.
see 049RC23.png
049RC23.log seems to be pretty useless.

Reproduction steps
-installing ros with VBEMP
-installing guest additions and rebooting then
-booting up (we have low colour depth initially) and selecting 32bit colour depth
-Installing Firefox

Another reboot will solve the issue.
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Please note, that this issue is been around for a very long time already (every build since at least 0.4.2rls was affected already, I guess it's no regression)