Post the entire contents of the CSS file (including the case-sensitive file name of the CSS file). And the beginning of one of the html files (starting with the <html> tag and going straight through and including several paragraphs that are exhibiting the white-space problem).
If every paragraph doesn't have the <br /> at the end of it, then something else must be wrong (either with the CSS itself—and/or how it's linked—or something else in the html).
The guessing and the "
after looking more closely"s are getting us nowhere.
Also, what are you viewing the ePub with when you see the white space? Is it only in Sigil's Book View or have you opened the ePub in ADE or any other programs? Please tell me that it's not the white space in Code View that you're trying to get rid of.