On-hit Effects Sometimes Become Permanent On Enemies

So I was playing Cho'Gath top vs a Teemo and I got a red buff from a fail gank from their jungler. I traded with Teemo and he ran off with the red buff animation (burning animation) and he went back to base. When he came back he still had the burning animation of the red buff, but he wasn't taking any damage from it.

I played another game against an Ashe, she used a health pot and went back to base, and when she came back she had the healing pot animation thing. This would stay until they go back into the fog. I don't think this is game-breaking but it sure is strange to see a flaming Teemo come from hell o.o