Bug with Vayne vs. Galio

I was playing support botlane, and we were doing fine, winning until 6, every time I ulted she was able to freely move around in my ult (didn't Tumble) and wasn't affected at all by it. My ADC noticed as well pretty baffled by it asking her how she could move during it without using Tumble or Tenacity or anything. Also, I ulted others like Nasus, Janna, etc. and they were all affected by it and would do zero damage to me - (literally they were attacking me and I wasn't losing any health) so am I missing something about certain champs being able to do damage/move freely during my ult? Did I experience a few glitches? Why was doing full dmg to me and others were hitting me doing 0 dmg? Insight would be much appreciated fellow Summoners <3