Force of Nature LOWERING unit cap (TFT)

I played a game earlier today in which I was lucky enough to get two force of natures. This correctly raised my unit cap by 2 for some time (from 7 to 9). At the end of one round, the game suddenly lowered my unit cap by 2, down to 7. I thought that selling and re-equiping the Force of Natures to a new unit might refresh the ability and get it working again. When I sold the unit holding them, my unit cap decreased by 2 (now down to 5 while being level 7). Re-equiping the Force of Natures brought my unit cap back up to my hero level.

The bug persisted through a few rounds, after which I died.

Both Force of Natures were equipped to the same unit, in case that matters.