I always have the same number of building licenses since i keep all mines running.
Today a copper mine ran out and a building license came back to the total.
For some reason it showed twice on the news feed, even though the other 5 mines were running.
I build a new copper mine and it took 2 building licenses from the total, so now i am short one from the total i always have when everything is built.

update: reloading the game didn't work, but logging off for a while and returning did fix it, must have been some sort of lag-related glitch.