I just finished a game in which my "Fleet : Frigates" stat went negative (and without hardly any losses, either). The only thing I can think of is that I had a MASS of Illuminators, and they used their 'ghost copy' (whatever it's called) ability a lot.
Could it be that when the fake copies die, they decrease the frigates-used stat?
The actual in-game fleet supply used did not have any problems, though.
