Source: http://world-of-ru.livejournal.com/2555477.html

Edit: THIS INFORMATION IS OBSOLETE AND THE DEVELOPER IN QUESTION WAS MISTAKEN

Well, this is interesting…

From Russian forums (a developer answer):

OrehMan: Well, you just confirmed it: if the player plays well – he gets to play on the bottom of the team, and if he’s a noob – he gets thrown on the top!

Inimigo (developer): “It doesn’t depend on general winrate, but on actual win series, player is less lucky – he gets put on the top of the team more often. If you pwn on top of the team without problems – try a more difficult task” (SS: in the sense that “we’ll make it more difficult for you”).

That certainly explains a lot. I am a bit skeptical about the answer (“lesser” developers have been known to not understand the inner MM workings), but still.

Edit: THIS INFORMATION IS OBSOLETE AND THE DEVELOPER IN QUESTION WAS MISTAKEN