[BUG] Tryndamere's ultimate being cast while in Guardian Angel stasis

This happens almost regulary to me - when in teamfight in lategame, I have Guardian Angel.
When my HP is going real low, I press R expecting to survive while my team finishes it. It often happens that I hear the ultimate being cast - yet I die and get into the stasis.

I think Guardian Angel fails from preventing the skill from being cast. Could anyone confirm it?