NFHS Rules interp

[dpomeroy]

Situation #6 in the 2001 NFHS Football Rules Interpretations
letter has our crew stumped: A1's pass is intercepted by
airborne B1 who is driven out of bounds by A2. While
airborne he throws the ball backward(don't you all love how
the NFHS comes up with plays that hopefully will never
happen?) and in #1 it is caught simultaneously by A&B
OR in #2 it just falls to the ground. The NFHS says in #1
it belongs to B but in #2 it is just incomplete. Our crew
understands #1, backward pass, simultaneous catch, belongs to passing team...but #2??? Why is it incomplete and A's ball back at the previous spot?