Just a quick pointer to a parallel discussion on the Processing board to see if I'm understanding Processing's internals correctly:
http://tinyurl.com/32hewkIt includes a pointer to the ruby file, and a test without subclassing, just calling PApplet directly .. which did not have the exception problem. This leads me to think exception handling works ok in the java classes, but not in a subclass of such a class. I think.
But no worries for now, let me dig a bit deeper.
Thanks for your patience.
Owen