Vayne q bug

So, a few days ago, i was playing sivir and a vayne was hunting me down. She wasnt too fed but i didnt have much mana so i run. At some point she caught up with her passive, used her q and hit me. Help was coming and i was at like, 90% health so i was good. But when the auto landed, i died. she didnt have a single w stack on me and my max health was 1634 i think. She had 349 ad and some crit with statik shiv. But the death recap said that her tumble (separate from statik shiv and other damage) dealt 1251 dmgand im pretty sure that tumble isnt the same as AA dmg so it was only the q bonus dmg that did that. I pretty sure this is a bug,cause i had like 50 armor too and she had no armor pen from items at least.

Rioters please notice this and fix it.