I split the new discussion (Sigil 0.9.x) away from the old thread, but left a link to it for reference.
First off: of the two people reporting this issue with Sigil 0.9.x, does this happen with all epubs all the time, or is it a random occurrence?
If it's not ALL epubs, does it always happen to the particular epubs it's ever happened to?
I think we're going to need some example epubs posted (no copyrighted material please!!) so we can see exactly what css is being used.
If copyrighted epubs are the only example you have, take a look at this
calibre plugin which was created for the express purpose of scrambling the text of books so copyright is not an issue when sharing said book for support purposes.
I would love to get this tracked down, but we've got to find a way to recreate it first.