This is how SSMS login is working for me and it does not seem to be correct.
Please follow these steps to reproduce this issue and replace <UserNameONE> and <UserNameTWO> with two of your actual user names.
Delete or rename SqlStudio.bin
Open SSMS and Login for the first time with Login: <UserNameONE> Password: <UserPasswordONE> and check the box to remember password.
Open SSMS and notice that the previous login of <UserNameONE> and the password is automatically displayed. This is what I would expect to happen.
Now login for the second time with a different user name and password. Login: <UserNameTWO> Password: <UserPasswordTWO> and check the box to remember password.
Now login for the third time with <UserNameONE> information. Login: <UserNameONE> Password: <UserPasswordONE> and check the box to remember password.
Now run SSMS again. I would expect to see <UserNameOne> displayed as that was the last user name that had logged in. However I see <UserNameTWO> displayed and this will never change unless you enter a competely new UserName which has not be used before to login to SSMS or delete SQLStudio.bin and start over.
Now no matter what I do each time that I run SSMS <UserNameTWO> will be automatically displayed in the Login box.
Is this the way it is supposed to work?