Crash when clearing "ans" variable in symbol table

[Michael Goffioul]

Hi,

While trying to run the "ad" package from octave-forge in my octave
(CVS, Windows+MSVC), I found that octave crashes when clearing
variables from the symbol table at the end of a user function evaluation
(ov-usr-fcn.cc:line 404). I could not reproduce the crash using a
simpler use-case, so I'll try to explain the context in which this happens.

I'm calling "__ga__ (stdout)" to run the test suite contained in __ga__.m
file (see 
http://octave.svn.sourceforge.net/viewvc/octave/trunk/octave-forge/extra/ad/inst/__ga__.m?revision=4487&view=markup).
This ends up calling test ("__ga__", "quiet", stdout), which runs the
test suite. As far as I could debug, the test function runs fine and exit
without any problem, then the interpreter gets back to the initial
__ga__ call. This function ends and the variable clearing takes place
(ov-usr-fcn.cc:line 404). One of the variable is "ans", but the problem is
that the "value_stack" of the corresponding symbol_record is empty.
The assignment at line 111 in symtab.h "varref () = octave_value ();"
calls varref(), which calls value_stack.top(), which crashes because
value_stack is empty.

I have no idea how to tackle this problem (I actually don't know what
*is* the problem: whether it's the fact that value_stack is empty, or
something else).

Michael.