I seem to have the same problems with AA.C$$m. In your case its easy to see they take the first two numbers (21) for your two inquiries and add the sum together (21 + 21 = 42), because you sought two different inquiries the computer cookies told AA.$$com that you are hell bent on getting this fare so on your next inquiry it took 21o + 212 = 42x (-2x ++x) = 24o
Hope this helps:

Really, the fine people at AA.$$com website have SERIOUS design errors on their FARE Pricing $$$ system. I can get almost any fare these days cheaper on competing websites rather than AA.C$$m. Whats really sad to me is its they seem to add fare $$ to any same day departure and return.
I have seen a difference of $600.00 Coast to Coast as compared to any competing website. 1000 bonus miles or not. In my opinion they should give 1000 bonus miles each time you use electronic checkin at the airport or print your boarding pass on your computer.

Good Luck!!