The session or access tokens or something from the new launcher system get invalidated every time I log in with the same account with a version of the old launcher system (including 3rd party launchers).

Steps to reproduce:

• Start the new launcher and log in normally.
• Close the launcher. (You can start the new launcher again, and you will be automatically logged in as is supposed to happen. Close the launcher.)
• Log in using the old vanilla launcher, or a 3rd party launcher such as MultiMC, using the same account. Close the game/launcher.
• Start the new launcher again, you will be thrown out and you need to retype your email and password and Log in again. (It says that you are logged in in another profile, and when I click Play, it throws me out with a "InvalidCredentialsException: Invalid token." error)

This is pretty frustrating, because it means that I need to log in again practically every time I start the new launcher, because I play a lot with older versions/instances (FTB/modded minecraft, using MultiMC).