Bug on Tryndamere R??? ;-;

Sooo.. i basically found out in a custom game with some friends that i was facing this enemy .. well let's say he was able to smite me and kill me when i used my ult... uhh last i checked ult is un kill-able for 5 seconds o-0... sooo like riot please check that? thank you .-.... seriously was soo confused when i was 1v1 ww he just smited me and then was able to kill me with my ult on and i had just clicked it. thank you <3 if you guys wish to try you can...