Based on what others have said about ebooks from S&S it appears the ones that do that are just poorly formatted.
That would be exactly it.
For what it's worth, the newer books from S&S seem to be okay; it's mainly the older titles that are problems.
If you're buying in ePub, anything from before late 2009 has a chance of being problematic. Some books they did a clean conversion from the extant OEBPS versions; others they converted from some other format (probably PDF), with miserable results.
With Kindle, the break may be earlier; however, I just went and looked at a handful of samples, and the same books that were fine in their OEBPS versions but are crap in ePub were also crap on Kindle. So "late 2009" may not be so far off after all.
(Random note: in a printed book, if the break is in the middle of the page, it's a blank line. If the break is at the top/bottom of a page, that's when they use the stars, since otherwise it could be hard to determine if there was or wasn't a break. New-to-electronic titles like SCE usually use all stars, while other titles in electronic form usually mimic their print counterparts - stars for stars, blanks for blanks).
Why they don't just take the damn file they print and turn it into a PDF is beyond me. Would have the exact same formatting of the physical book.
They used to do that, but nobody bought PDFs because they're terrible for use on mobile devices. They might work better on modern eInk devices, but they still wouldn't be good reading experiences (no ability to change the font size, lots of unused space on the screen, etc.).