Booking a domestic leg in I (first class) as part of a TATL saver business award recently caused the award level to go from 100K to 117.5K. After much discussion with a couple of res agents who could not understand the problem, I had them change the booking class in the domestic segment from I to IN and it fixed the problem - 100K miles as it should be.

So there is a difference between I and IN booking class, but more likely a problem with the UA booking system.