Found a little glitch. Granted, it's caused by my screwup, but it might be an easy fix.
The problem: Select all your xhtml files in book browser. Rename, and type in something that would produce a filename error, such as '.html/' (yes, I have less nimble fingers sometimes and my fingers are moving too fast to catch the error before I hit the enter key...) Sigil correctly admonishes me with an error 'A filename cannot contains [sic] the character "/".' BUT, like an old female horse, it continues to admonish me for EVERY file I had selected....
The possible solution: can you exit the rename loop on the first error instead??