I am citing the man himself:
Hi guys, I have seen a bug in the MM, some may call it a glitch, as far as I know, if you open a platoon with just yourself in it, it seems like you always get top tier MM, no matter what! I’ve tried this and asked friends to do it as well, and it seemed to work, at least on EU on 09/05/2017. I’ve sent a ticket to Wargaming support, but I think the more the best, so could you guys try it out see if you get the same thing as me, and if so send a ticket too? I don’t like this as it gives some players an advantage they shouldn’t get.
Here are some examples I got https://docs.google.com/document/d/1TO779cqrCy7i412Xa4FgdO7ZC-1UHJclI1-9kDkd1fI/edit?usp=sharing
As far as I know, WG is working on fixing this, so make sure to abuse this bug as much as you can. And a reminder: it seems to not work on some tanks.
And I say this since so far, no players were banned for abusing bugs. So it’s not likely they will do that to us.
Anton Pankov on the bug:
„The problem is known, there is already a fix coming soon. Thank you for paying attention to the problem.”