I have experienced this problem of finding an apparent bug in a large piece of source code but being unable to write a test program to demonstrate it. My approach was to take the actual application and successively carve chunks out of it, checking whether the bug was still present. It took about half a day to do but did eventually end up with a small test program that enabled Frank to fix a bug.
I might try this; it may or may not happen today, but at some point in the near future, I will make a duplicate copy of my program, undo the 'workarounds', and start chopping away at it, to try to minimize the size of the program that still exhibits the unwanted behavior. If successful, I will send a reply to the list with my findings, and depending on the size of the remaining source code, just send it out (list if only a few K, otherwise to Frank's private address).
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