@tshering: Hmm. Strange, I couldn't reproduce it on ARM either. (EDIT: Which binary did you use? The K5 one should be the closest one, although softfp, not that it matters that much here).
[EDITē: Meh, my bad, I only put a single binary in there. Keep the previous comment in mind for when I'll update the package, though].
Well, the good news is, it was slightly off in every cases anyway, so I ended up porting KOReader's maths (again ;p).
I'm making sure that I didn't break anything in Kindle-land, and I'll update the post

.