After launching a sketch from the PDE (either by hitting the run button,
selecting run from the Sketch menu or using Ctrl+R), keyboard input is
completely disabled until restarting Processing.

One workaround I found to avoid restarting Processing, is to create a new
sketch, which I then close. For some reason this action restores keyboard
input in the original sketch (until it is launched again).

I have seen this bug only in Ubuntu Linux (9.04).

i believe this is a window manager problem. i seem to remember it coming up
before but i can't find the bug report for it. something about turning off
effects or something like that.

Thanks for the comment.

I have all the 3D eye candy effects turned off (i.e.: compiz), but I'll see
if there is any other wm parameter that can be tweaked to solve the problem