It looks like this commit added the 2 pixels :
http://websvn.kde.org/branches/trinity/3.5.13_frozen/kdebase/kicker/taskbar…
I guess it's something related to the QT4 port of TQT. You
can try to
revert all the "-2" in the code and recompile to see if it
fixes your issue.
Now, how did you find that?!
Sure, I'll see what happens.
Darrell