May not be the same problem but i cant use alt tab unless i first use shift tab ingame. Is this the same for you bootkiller?
ubuntu 12.10 64b
No, it doesn't work even inside the overlay.
This isn't only specific to KDE. I can't alt-tab on Windows either.
The release today has fixes for this. On win32 and OSX the topmost bit is removed from the game, so you can alt-tab. On linux you may also need to set "cl_mousegrab 0" to enable alt-tab, depending on your window manager.
Nothing extracted yet.
I'm currently unable to alt-tab with Counter-Strike unless I disable desktop effects, it is working fine on TF2 and other games on Steam.
System Information:
https://gist.github.com/4642430
KDE 4.9.98