Since I backdated to Sigil 1.9, no problems. Although I like Sigil, am still looking for a good epub editor for the Mac, one that doesn't require me to unzip the epub file. I found a bit of a rusty program for the Mac from Adobe, PDFXML Inspector, that runs under Adobe AIR. It isn't a wysywig editor, but it does let you inspect the whole ePub file and make edits to it.
Both AIR and PDFXML Inspector are free downloads.