Debugging dragDrop handler crashes Metacard

[David Epstein]

Using MC2.5 on OSX 10.2, I am writing a fairly complicated "dragDrop"
handler, which decides what text to insert at the dropChunk, and
whether to preserve or delete the chunk that was originally dragged,
and then carries out those decisions.  I'm handling and not passing
both the dragEnd and dragDrop messages, thus overriding MC's default
decisions about what to insert and what to delete.

The problem I have is that when I use the debugger on my dragDrop
handler MC pretty consistently experiences an "unexpected" quit. 
Typically, I'll manually set a breakpoint, do a dragDrop that triggers
the handler, step through some lines of the script and study the
variable watcher; and then choose either "run" or "abort."  Either
way, "Metacard has unexpectedly quit."  Indeed I can step through the
entire script, and when we seem to have arrived safely at the
end--with no evident errors or problems--MC quits.  This happens even
in cases where running the script without a breakpoint causes no
error.

Anyone have experiences like this, or a theory of how to avoid them?