Last night I won about 4 games on Dota 2. The games were completely unbalanced to our side and I "trolled" a bit, but nothing special.
All of the games were added to my loss counter rather than my wins. Does anyone know why it is happening?
It seems a bug. If your game history, as suggested by @yx in comments, registered the matches as wins for your team, submit the bug to Dota 2 Beta dev forum. Copy down the IDs of your matches to let the devs check easier what went wrong.