> > ps you have an example, or what you think is an example? 
> > That I can try?
> 
> Take a 3.6 alpha open some windows, browser, then invoke a 
> deprecated method such as Smalltalk beep. When you proceed
> the notifier, you have a big chance to see all the panes
> getting refresh extremely slowly one after the one
> ones even those that should not get redrawn.

You can almost certainly make it happen by adding "Processor yield" as the
first line in Debugger>>resumeProcess: - it all looks as if there's a
confusion between which of the processes (the debugged or the active one) is
the "UI process" here. I would suspect that the Mac VM (being
multi-threaded) issues a signal on the input semaphore which invokes a
process switch very similar to adding Processor yield in #resumeProcess:.

Cheers,
  - Andreas