[Pharo-project] Debugging code with morphic leads to freezes and a weird message

While debugging actions behind buttons, I do get Project class>>spawnNewProcessIfThisIsUI: not being understood. This prevents from debugging interactions properly. And sometimes I get the dreaded "Computation Terminated" message, effectively locking me out of the image (nothing moves anymore, I've got to kill the process). Ideas on how to fix? This is 1.4 14438 -- Philippe Back