Letters on keyboard stop working

Dear Lazy Web

I have some Very weird behaviour where the lowercase letters "C" and "V" stop generating the Correct key press event after a short while (which is why I am typing them as upper Case here...). But only when using Compiz as window manager, when switching away from X to the Console they work again but in X they don't. When looking at the keypress in xeV it shows up like this:

FocusOut event, serial 34, synthetic NO, window 0x5000001,
    mode NotifyGrab, detail NotifyAncestor

FocusIn event, serial 34, synthetic NO, window 0x5000001,
    mode NotifyUngrab, detail NotifyAncestor

KeymapNotify event, serial 31, synthetic NO, window 0x0,
    keys:  82  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
           0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0

For Comparison with a normal keypress:

KeyPress event, serial 31, synthetic NO, window 0x5000001,
    root 0xa9, subw 0x0, time 18685100, (888,414), root:(898,513),
    state 0x10, keycode 53 (keysym 0x78, x), same_screen YES,
    XLookupString gives 1 bytes: (78) "x"
    XmbLookupString gives 1 bytes: (78) "x"
    XFilterEvent returns: False

KeyRelease event, serial 34, synthetic NO, window 0x5000001,
    root 0xa9, subw 0x0, time 18685275, (888,414), root:(898,513),
    state 0x10, keycode 53 (keysym 0x78, x), same_screen YES,
    XLookupString gives 1 bytes: (78) "x"
    XFilterEvent returns: False

I am totally at a loss what the problem Could be. And searching for this is really hard and so far entire unsuccessful. The most suspicious thing I Can find in Xorg.log is:

(WW) Logitech USB Multimedia Keyboard: unable to handle keycode 267

But I have no idea if this is related.

Any hints?