Now I understand your point (I really shouldn't try to answer questions before my 3rd cup of tea in the morning, which I was guilty of with my previous response). Thanks for spelling it out for me.
In debug mode there are things that happen that might lead to crashes not happening, as I'm sure you're aware (for instance, uninitialised memory gets zeroed out, which means certain checks work in debug but not in release). So that's understandable, even if it'll probably be tricky to track down.
As for fibers on vs. off... I can see this is a bit strange, but it makes sense when I see that you're working across multiple documents. It's very likely that there's a problem with the way you're currently coordinating documents that doesn't occur when fibers are off, as things are working a bit differently. It sounds as though this needs some deeper analysis, especially if you get problems once the code finishes.
Thanks for your patience - I should have really understood your point sooner, looking back. Unfortunately I don't have a magic answer, though.
Kean