PR# 17686 Zone becomes a black hole

With 6.6.86627 (on both Solaris SPARC and OpenSolaris x86), I have found
that repeatedly and quickly moving tools around both within a zone and to
another zone eventually (sometimes right away, sometimes after several minutes
of this repeated moving) causes a zone to become a black hole.  None of the
tabs within that zone can be moved out of the zone, though they can be moved
to different positions within the zone (e.g., a tab can be moved to the left
or right of where it is).  When this happens, other tools can be moved into
this zone, but then they too become stuck there, unable to escape.  In fact,
the zone itself cannot be moved out of the main window when this occurs.
Resetting tools layout always seems to cure the problem.

If you could suggest what I should look at in the debugger when this happens
(I think I can make it happen when running "ec -gui" from within estudio),
I can try to investigate further.

Repeatedly and quickly move tools around, both within a zone and to a
different zone or undocked from the main window altogether.  Eventually, a
zone from which one is trying to move a tool becomes a "black hole".