Originally Posted by tkirke
Perhaps it's the fact that each table of contents items is the has a link to a different xhtml file?
Yes, that will force a page-break as the reader loads the file. If you don't want page-breaks then the next chapter needs to be part of the same file, give it a fragment identifier (<h2 id="chapter x">) and you can still reference it from the ToC.
Since MobileADE require each file to be under 300k when uncompressed, you'll need to have separate files (with inevitable page breaks) at some point if your book is long.