Black/mirrored upper left corner → Bug... ¿?
Before I report this as a bug I wanted to have some confirmation that this indeed is a general issue...
It is a bit strange, but really reproducible on my system (quite consistently I must add). If I try to launch pretty much any game (except from a few ones like the The Book of Unwritten Tales and Journey Down) straight off their launchers (aka .desktop files), a little black rectangle lingers in at the upper-left corner of the screen, depending on the DE I launch the game from (tested if this had to do with composition being used, i.e. XFCE instead of Cinnamon or G-Shell). However launching the games within Steam (i.e launching Steam first, THEN launch the game) this will not happen. This happens even if I close the game, go back to Steam (launched with the game) and try again this time within Steam, it would still have this issue... Even the Steam menu bar is "affected" by this black rectangle obscuring the Steam menu item.
Now this happens with Steam 1367621987 / 13676219... (I guess there should be more numbers there, just the window doesn't show 'em), but been having this ever since the Beta, so I know I have to launch the games AFTER I launch Steam, but regardless I test every now and then. Anyone else seeing this on their Steam?
System configuration and software combination:
OS Fedora 18 x86_64 fully updated to 2.8.11-200.fc18.x86_64 kernel; 32-bit libs dependencies covered (with 0 multilib issues thus far, and ever since I migrated to 64-bit Linux back in 2k4)
AMD FX 6100 CPU
nVidia GeForce 9800GT 512MiB gfx with proprietary driver version 304.88 (yes a tad old, but they work very well on this gfx)