Sorry I never got back... everything has been a bear. But FTR Sigil ended up crashing again (when placing an image) after I wrote last, even without long filenames, but it was the last of the image-placing portion of the project and I had to move on. And now it's been so long, I can't remember if thumbnails were turned off... I thought I had them turned off after Kevin suggested it, but maybe they were turned on for testing and I'd forgotten. IAC I only remember thinking, "No wonder DiapDealer couldn't get it to fail."
Hopefully after publishing I will have more time. Right now I have another problem (no, not crashing

) but have to start a new thread for that. But yeah... the long filenames ended up
not being the answer to this particular problem. Maybe it IS just some conflict on my system. Wanted to at least report that until more can be done!