Yes, I can confirm the bug you're reporting: 'nmi' is seen as nano-mile instead of nautical mile. Sorry about that!
I need to see how to address this. You can fix this locally by doing the following:
1) Tap the My Data tab, tap Units
2) Tap the Edit button
3) Tap the Length [m] entry
4) Tap the Definition line and scroll quite a bit to the right until you come to the entry for "Nautical Mile [nmi]"
5) Change that text to "NauticalMile [Nmi]"
6) Tap the Save button, tap Done
You can now go back to the calculator tab and do a conversion like this
and it will correctly return 0.86897...
Hope this helps.