Seems to be another idiotic Gnome thing. Luckily they weren't stupid enough to not make it optional. Look on the keyboard settings screen. There you can select something like 'key down will fake key presses'.
This and the inability to add the volume manager (and of course the stupid shit Gnome already had) made me go back to KDE after half an hour.
I don't know about alt-f4 though. But you can except the worst.