If slow filters are disabled, then a best score is achieved in a track, then slow filters are re-enabled, and the 'A' key is pressed to reset to the best position, the score shown is the score with the slow filters disabled, not with slow filters enabled.
That's the reason the devs introduced "Restore Crdt Best" (Hotkey "I") back in the days the problem of invalid best scores made its first appearance.
Useful once the bug is fixed.
I should have been clearer in my description of the problem: I get credit when I should not. Silverberg's feedback http://fold.it/portal/node/994707 is the same problem, and has got the devs attention.