To confirm my point of view, see Morph>>privateAddMorph:atIndex:

It manipulates a submorphs collection without guarding it with semaphore.
It really likely that tight loops running in multiple processes may
damage collection, especially when you using Delays which enables
scheduler to switch processes at any point.
Also, i'm sure this is not the only place, where breakage can occur.
Morphic is too complex to say something definitely.

To summarize: manipulating morphs using concurrent code is a big no-no :)

-- 
Best regards,
Igor Stasenko AKA sig.