windows 7 - Alt+Tab behaves like Alt is sticking (but it is not)

Sometimes, when I press Alt+Tab and then release, the window select menu stays up until I chose a window with mouse or press Enter. Just like if I wouldn't let Alt key go (but I do). Anyone has an idea why this could be the case?

1. My keybord is brand new (3 days old). Also I opened screen keyboard and see when Alt/Ctrl/Shift/Win keys are pressed and when they are not. So I'm sure none of those 4 keys are sticking by any mechanical reason.




2. The behavior is "localy stable". I.e. it works many times in a row. And then (when I forget about it) it behaves normaly many times in a row.




3. I doesn't it when switching from specific windows. But those specific windows are different each time. I mean when it starts to "stick" it sticks all the time for some windows A,B,C and doesn't stick for D,E,F; then it stop to stick and starts again in a while and now it sticks for A,E,F and doesn't stick for B,C,D.




4. It behaves in the same way with left and right Alt.




5. I use SharpKeys to remap control keys. Caps -> Left Ctrl, Left Alt -> Left Ctrl, Left Ctrl -> Left Win, Left Win->Right Alt.




6. I have sticky-keys disabled.

Answer

I have discovered that that happended only when a top window is in foreing keyboard layout (I've tried Greek, Russian, German). When I switched layout of the top window to English I could use AltTab normally.

Then I was able to check if this disappears when I turn off SharpKeys (thanks to @JaredT for the hint). And I've found out that the problem was that my Right Alt on my keyboard is actually Alt Gr. So when I used SharpKeys I actually used AltGr+Tab instead of Alt+Tab. Once I've rebinded to use Left Alt instead of Right everything started to work fine.

So I guess AltGr makes Tab to mean something different when you use layout different from English.