Possible Lucian Ult Bug

I seen this twice in a game so I am not sure if it can be reproduced or someone can confirm, but Lucian ult someone who is stepping on thresh wall, it seem to negate all his dmg until the slow from the wall the over. I noticed twice in one game of ranked where my Thresh would ult and as I ult the same target, the target did not take any dmg when they hit thresh wall and only took time a short time after. Not sure if it is framerate lag but it seems somehow thresh wall negate the culling's damage.