maybe SAB is adjusting the html to be ebay-compliant, then? (course, it's not adjusting it 100% since scroll bar colors have been customized, which is against ebay rules)
does sound like, though, that SAB is altering the code to keep the background contained.
the way the html is written, auctiva's version is the correct version. but the SAB version is more in line with ebay regs since ebay says you are not to change anything outside of the description box area.