Was waylaid for the last 5 days on other matters so could not work on the book until today. Sigil crashed 3 or 4 times, in the same manner as previously described. This is with Sigil's temp in the native location.
Can't fool with it anymore for now (have to get this book done) so am just using CTR S constantly, especially before placing pictures. But later when I have time I will resurrect this thread or if I happen to figure out what's causing it along the way inadvertently, I will report that. Since the Sigil team says Sigil is stable I can only guess it's a software conflict on my machine, which would nevertheless be handy to know. So again... if I happen to suss out the problem, I'll be back.... but in a total non-Arnold-Schwartenegger way.