Guardian Angel Zilean Bug on AR URF 2016

I was playing AR URF this last Sunday when I bought a so that I could be unkillable as Zilean. It worked fine when I died (I "died" and came back to life) but when I looked at my health bar and stuff, I noticed that I had mana. Yes, I know there's still mana bars in URF but my mana bars showed that I had spent mana but when I used my other abilities, the bar didn't decrease. Anyone else encounter this problem?