Regression of r75407, Rocks&Diamonds 3.3.1.2 from rapps leaves its taskbar visible when switching into fullscreen via alt+enter

affected 0.4.11-RC-25-gd332edc gcc dbg linux
on VBox 4.3.12 + VBEMP

Reproduction steps
-set desktop resolution to 800x600 32bit
-Install Rocks&Diamonds 3.3.1.2 from rapps
-run the game, it will start in windowed mode
-when in main menu, hit alt+enter to switch into fullscreen mode

Expected result
The game switches into fullscreen and the taskbar is hidden
r75406_ok.png
r75406_ok.log

Observed result
The game switches into fullscreen and the taskbar remains visible
r75407_broken.png
r75407_broken.log

A regression, guilty revision is SVN r75407 == git 0.4.6-dev-g09ab5ea7ed2ab0e709ed2e8f8f9f6c3711b2ac7f