It maximise the total clicks your account get I recon, but not maximising the total click a keyword gets.
My guess is that it disabled a high cost keyword, in order to have more clicks on lower costing keywords.
Actually I started very low and decided to let the optimiser set the optimal CPC. It kept some, edged some up, sent one through the roof, and lowered the now two offending ones below its self imposed threshold for inactivity.
But it is meant to optimise! And the inactive keywords do not look as if many people would compete for them.