Yep, by themselves they work fine.

Also, an update: I managed to get your example to work (I had to pack the frame instead of gridding it). However, my output is different:

As you can see, my computer treats holding down the 'a' key as pressing and releasing it over and over (instead of just pressing it). As such, I don't really see a way to code what I want, as there's no way of determining what the final KeyRelease action is (unless there's some way of testing whether a key's been pressed in the last X milliseconds, then I could act only when it hasn't been, although there'd be a delay).

However, I've found an easy way out for now: it works fine with mouse button presses.