LBreakout 2.6.3 when alt+tabbing out of fullscreen, a tile is left in top-left area of desktop

0.4.10-RC-29-gf6a9392 gcc dbg lin
VBox 4.3.12, VBEMP

LBreakout 2.6.3 is an SDL app.

Reproduction steps:
-switch it to fullscreen
-Hit alt-tab to switch back to desktop

It will erroneously display a tile on top left of desktop, that has the same size as a tile on Explorers task-bar.
tileTopLeft.png
0.4.10-RC-29-gf6a9392__LBreakout263_tile.log

This was broken since ages. But currently it is not coupled with that many other side effects, so I decided to limit this ticket to that individual tile-problem.

Can also be seen in some other apps.