It will only be a bug if the university actually completes in one turn, because then it is a huge exploit!
I suspect what happened is that you completed something for which there were additional production bonuses (stone, marble, leader traits, etc. . .) . Since those bonuses don't apply to the University, the game is adjusting the overflow and ending up (somehow) at -2 hammers.
-2 *1.5 (forge+Org Rel.)= -3
the # of turns to complete is cost/adj. production, but cannot be less than 1. Any positive number divided by a negative number is less than 1, so 1 is what the game displays.
Like I said - if the Uni completes, it's really problematic. . .