I could not kill 
barrels with my clean cut auto attacks after I used an ability and gained my passive. Happened to me multiple times in the same game. However I was able to kill the barrels when my passive was not active.
Vedius5 votesWorks on Illaoi tentacles and yorick wall as well. Made a post a couple days ago hoping someone could get this fixed.
Parafex4 votesWas about to post this, +1 if passive is active the auto attacks go through the barrel and don't destroy them, You have to wait till the passive is over, Pretty annoying.
Sir Gucci XIV4 votesJust encountered this as well. +1
13900 Essence4 votesAlso the same for kalista ghosts, it is probably this way for any champion-made things that are auto-attackable. Riot spaghetti at it's finest.
Isajohoff4 votesI've had the same happen. This is a game-breaking bug - a well-timed auto on a GP barrel can make or break the final teamfight - I don't know why this hasn't been fixed yet.
Can someone test if the same thing happens with Twitch R? I could imagine the effect being similar.
CatastrophiX3 votesI've had it happen a couple times. Pretty stupid. If you cant shut the barrels down it kills you
Guiboulou2 votesAs multiple people have already said, the same happens with a bunch of other player-made entities. Your report is far from the only one. I'm kind of baffled by the radio silence on this one...