Ah, so that's a book of your own making. Yes, I can confirm similar issues with e-books created by myself; properties like margin-top, margin-bottom frequently get disrespected by all kinds of e-reader software. The best e-reader I know, Marvin for iOS, also used to have this particular issue, but after users complained, Marvin's developer fixed it so that now, margin-top and margin-bottom settings seem to be consistently respected even when outside of Marvin's "publisher mode", and even after the user adjusts the default paragraph spacing. Perhaps it wouldn't hurt to notify the Moon+ developer of this issue.
PS: Ah! That's DiapDealer replying now, not davire.
In any case, I'd try reducing paragraph spacing first, in davire's book, to see what happens.