(*Edit*) I've just restarted the client a couple of times and two of the duplicates have vanished but I still have one duplication for this mission. Whilst this is a minor issue I still find it odd that it's persisting for this long.
So, I'm aware that a day or two ago there was a bug that prevented progress being shown for the current set of missions and that that was supposed to have been fixed. Why is it then, that I've logged into League of Legends today to find that I have 4 new missions but their ALL the same? I have the initial "Fight for your house" mission which I've had since the event has been on and that's been resetting as normal upon it's completion, except now I have 3 **_extra missions of the same name_**. Additionally, 2 of these missions show that I have made no progress towards winning either the 1 SR or 2 ARAM games whilst the other two show that I have already completed it, yet have not vanished from the mission tab.
Riot, care to explain why your supposed "fix" has caused another bug or two?
P.S if someone is able to explain how I can take a screenshot of my League of Legends client to provide the evidence then please leave some instructions below and I will show the bug as it is currently appearing on my client.