This seems to be related to the bug where more tactics build then you can actually hold, but they sit in the armory. So every time you use and rebuild all your tactics, it could be rebuilding up to twice as many as you can hold. Even one means it is rebuilding all you can hold plus one, so it credits you for each of those as the timer finishes on them.
On the other hand, this provides a small amount of balance to the absolutely ridiculous number of tactics that get set as a goal.