Killed by smite during Tryndamere's ult

A few days ago I was playing as Tryndamere top lane and winning lane pretty hard. Warwick the enemy jungler came top and I ulted to stop myself from dying yet when Warwick smited me I died. This is a bug and should not happen. I do not know of a single ability or spell other than this that can kill a Tryndamere whilst he is ulting. And I quote, "Tryndamere becomes immune to death for 5 seconds during which his health cannot fall below 1." I know Tryndamere is not a champion that is played often, so this may be over looked, but as one of my main champions and a champion I have a lot of fun playing I hope this is fixed soon. If Video proof is needed I can get this in a custom sometime by the end of this week.