Looks like the QueryResultKey has a bug when it creates the hashCode for the filters.
This bug is in 4x and trunk. Unless I'm missing something, the code is calling hashCode on the list of Queries rather then the individual queries.
Nice catch Joel!
I've added a super simple test for this.
Thanks Joel! Tossed this in 4.2.1 as well - kind of a nasty bug really.
Closed after release.