This is a new one to me, but four of my students can reproduce it
every time with Mac OS 10.6, with or without JACK, using Pd-Extended
0.41.4. Unplugging or plugging the headphones while Pd is running
freezes Pd completely, requiring a Force Quit. It does this regardless
of whether audio processing is turned on or off. I tried looking at
Aggregate Devices, however the built-in output already appears as one
device. Anybody know how to fix this one?

D.