Tkinter -- interpreter crashes in tcl in presence of threads?

[Bernard Sufrin]

I've been plagued, across two very different programs, a few variants of
python (1.6, 2.0, 2.1.1) and tk with what look like tcl interpreter
crashes during a python call to tcl at an unpredictable time during the
execution of the program.

The error report is always along the following lines:

TclExecuteByteCode: done instruction at pc 4: stack top 0 != entry stack
top -1
  Source: "5067420callit"TclExecuteByteCode execution failure: end stack
top != start stack top
Abort

The only thing the programs have in common is that they use threads as
well as having a Tkinter mainloop active. In all the programs,
invocation of Tk code is done via an agent thread (so there's no
immediately apparent race for Tk resources between threads.).
One of the programs is doing event simulation, the other provides the
user-interface component of a proof assistant.

In all cases I'm using the stock python libraries, and a stock tk/tcl
setup. In other words I can't put this down to some imported (or
self-written) extensions to the libraries.

Can anyone shed any insight into this?

Bernard Sufrin