Game switches to another account while starting the game

I have two accounts (premium) - "Lemafor" and secret (I don't want to publish the name of the second account). When I try to change the account to the second account all is OK in the launcher. But after start I see that MC uses the first account (Lemafor) - both in SP and multiplayer.
Two weeks ago it was OK, I could use both accounts. But today I don't know how to start MC with the second account.