And here's a slightly less broken MU patch, that attempts to kill the extra StartOffsets in the mobi8 part when splitting (and tries to avoid the guide entries without title in mobi8 in a slightly less stupid way than my previous attempt)...
@Tugger: Keep in mind that (some) devices handle those (master mobis with multiple StartOffsets) files fine, not only the Previewer. It works correctly on my Touch. Only FW 3.4 (and possibly 4.1?) seem to be confused by these files.
And with this patch, you can end up with a mobi7 & a mobi8 that should (hopefully) work as well as if they were processed by the KDP.
EDIT: Updated patch in #53