Glacial effect sometimes heals enemies

There is a bug with glacial which causes it to heal the enemy it is applied to sometimes. I have only had it happen in one game so far, but it took my three characters (ashe, vayne with a frozen mallet, and sejuani) a very long time to 3v1 a tristana because she was repeatedly pushed to full life by the glacial freeze being applied. It also seemed to buff the character's health (the health bar would gain bars) but I wasn't looking at the numbers so I'm not really sure if that is the case. I eventually lost to damage taken from timeouts as I simply could not kill my opponents' characters with the constant full heals they were receiving from the glacial effect. It seems to be the case that the bug comes from multiple instances of freeze being stacked on top of each other, as I never noticed it happening on the first application of the freeze. So far I have been unable to recreate the bug but I'll probably keep using glacial as it's broken beyond all belief and add an update if I see it again.

Edit: If it helps at all I did have 6 glacials in that game (ashe, anivia, braum, lissanda, sejuani, and a vayne with mallet)