It's working like it should. When you create a new account and play Lone Wolves, the vast majority of the players in there are solidly set into their rank. When you beat them, it doesn't consitute a large increase in trueskill. When you beat other fresh accounts, you'll notice you rank faster.
The difference is in this playlist, there is nobody on your team which the system can place into perspective your trueskill. You face a bunch of low sigma players.