Eclipse 4.2.0, PyDev 2.6.0, 64-bit Ubuntu 12.04
1) start Eclipse/Pydev and enter some python code
2) try to press Ctrl+3 to comment some code and Ctrl+Shift+3 to uncomment - works
3) select some block and add comment block by Ctrl+4, uncomment it using menu - works
4) try to press Ctlr+3 to comment some line - it does not work, it actully works as Ctrl+Shift+3 being pressed.
I am not completely sure about which activity triggers this bug, it might be slighlty different than point 3 above, but it definetely involves block comments and corresponding menu. It seems to me that this "sticky" Shift has also effect on some (but not all) other key combinations.