Originally Posted by
mduell
I suspect it's a bug rather than demand-exploitation; something like:
If you're an elite, it looks for the cheapest B fare (M for 1K), since someone assumed coach would always be cheaper than first and elites are instant upgrade eligible.
If you're non-elite, it looks for the cheapest first fare, and it's finding UP/UPDI fares that are way cheaper than B.
Just checked in my 1K SO for her SAN--SFO flight and upgraded her for $149 from G (only 2 seats left, so Mr. Wonderful took care of any uncertainty).
She's now in P, so it definitely didn't restrict the search to Y/B/M.