You write some code on the actions panel. You test your movie. You close your movie with command + W. The cursor still remains on the actions panel blinking but the focus is on the stage…
So if you press any key like “del” you’re deleting a movieclip instead of code.
Instead you have to grab your mouse again, click on the actions panel, and go back to your keyboard. ARGH
Yeah, sucks big time, I run into this problem constantly.
Spaces is another issue with CS3.
I suspect it’s probably a Leopard issue, since other app focusing weirdness exists with that system.