Xayah passive does not hit Gangplanks barrels

I first saw this in a 5v5 norms on summs rift. I asked a friend to help me duplicate it and we were able to.

1. Have Gangplank place barrels on the ground (it does not matter how many stacks are on it)
2. Have xayah Start deadly plummage, and cast it.
3. Attack barrels, your auto will pass through the barrel and not do damage till the passive falls off.
4. Rinse, repeat.

I downloaded the game replay. If you need a replay put on YouTube or something let me know. Please help.