How do I setup description_list properly without having invalid username error

I'm running Toad 12.6.0.53 and I'm working on two databases which contain the same setup - but are not clones as the schemanames vary between the two databases.

As in 99% of the time it is NOT important to which database you acctually log in, but only the schemaname is important i tried to setup my local tnsnames like the follwoing:

MYDataBase=
(DESCRIPTION_LIST=
  (DESCRIPTION=
    (ADDRESS=
      (PROTOCOL=TCP)
      (HOST=MyIP1)
      (PORT=MyPort1)
    )
    (CONNECT_DATA=
      (SERVICE_NAME=DatabaseName)
    )
  )
  (DESCRIPTION=
    (ADDRESS=
      (PROTOCOL=TCP)
      (HOST=MyIP2)
      (PORT=MyPort2)
    )
    (CONNECT_DATA=
      (SERVICE_NAME=DatabaseName)
    )
  )
)

So now I can logon to the two database by only giving the right schemaname and password for that schema. Only that I cannot. Toad will eventually give me an "ORA-01017: invalid username/password; logon denied". After trying it a couple of times, Toad will then be able to connect without prompting for a password anymore.

Do you guys now why that might be?

Kind regards