6 Mage Buff

I'm currently in a game, where I have 5 mages on the board, but getting the 6 mage buff.

https://i.imgur.com/0z9EaD2.jpg

As you can see, LeBlanc is on my bench but the buff is still active. In the post match screen it also only counts 5 mages: https://i.imgur.com/1d1nnYo.png

This isn't merely a visual bug as all my mages were in fact casting all their spells twice with one cast.

Not sure how to replicate... but it started when I had three mages on the board: LeBlanc, Vladimir and Taliyah. Both Vlad and Taliyah were lvl 2, LB lvl 1. As soon as I got Veigar, I replaced LB with him. That's where the bug started, as I replaced LB with Veigar the Mage count went up from 3 to 4. Later on I got Brand and Syndra to get the full 6 Mage buff. This is also how I found out it's not just a visual bug.