There are 3 effects of the bug:
1: Unit icons on the map get a thick, black, blinking border.
2: Shots, explosions, burning, smoke, tree details when zoomed out and shields blink or even become invisible.
3: Nano smoke blinks or becomes invisible.
Sometimes only some effects appear, but usually all or noone. If a higher numbered effect appears, lower numbered effects usually appear too, but not always. Wheter the effects appear also depends on the zoom (effect 1 is usually better at mid zoom, 2 when zoomed out), but usually it appears on every zoom.
The bug can be fixed by deleting Spring/LuaUI folder or all zk_... files in Spring/LuaUI. Then all GUI customization is deleted, too. When I start to reconfigure my GUI, the bug returns pertinaciously after short time. The bug also returns in the second game, when GUI is not changed.
While certain sets of units are selected, the bug doesn't appear temporarily. The required size of the set varies. Sometimes even a single unit is enough, but not every unit. It seems as if an eco structure must be selected. I could probably fix the bug by definig a mex as a unit group and define a MouseButton as (Ctrl+[number of the unit group] - Ctrl+LeftMouseClick) and use this button to select units + a mex by default.^^
After some time there was also a game with only effect 2 in a very strong way (mostly disappearing instead of blinking), that could not be avoided by selection.
Do you know a better solution to this problem? Probably just reinstall.. I didn't change any hardware or drivers, when the problem occured. Thx for replies.