Blue tit nest building in August??!

So confused, I had a rooster in one of my side boxes lastnight, I cleared all my boxes out the end of last month when the sparrows had their last brood.
Anyway this morning, This female blue tit is bringing material into the side box she slept in lastnight! 
As she picked this box for spring already? turned my camera on this morning to see moss in the box and her bringing a beak full in must say its shocked me, Never happened before.

Just put little video of her in the box on twitter