[GAMEPLAY] Twitch ult bugged while attacking enemy nexus

In Howling abyss while backdooring, I activated my ultimate for the extra damage, but after that, I could not deal any damage to the enemy nexus. I could kill minions, I could attack, but the nexus without dealing any damage. I needed to wait till my ultimate was over. I'm not 100% sure that this is a bug, maybe it's meant to be like this, but then I think it's a bit stupid that we can autoattack it, and it should be stated in the description of the ultimate.

After a bit of digging I found out that there were a lot of similar cases in the past year. Even the LOL wikia page contains information about this (http://leagueoflegends.wikia.com/wiki/Twitch) : "Twitch's attacks will pass through structures and terrain, but will not damage structures unless they were directly targeted for the attack. The exception is the Nexus - Twitch's attacks will not deal any damage to it. This is likely a bug."