That's not a bug; it's a design limitation.
You can log in only two levels deep without entering a password again. You can login as reseller and then log in as a user without ending a password again, or you can login as admin and then log in as a user without ending a password again, or you can login as admin and then log in as a reseller without entering a password again.
If you've logged in as reseller and need to log in as the user and don't know the password, then exit the reseller login, which will put you back into the admi login. Then login as the user from there.
You can also, from the main DirectAdmin log inscreen login as
admin|username to login directly as the user if you only know the admin password, or as reseller|username to login directly as the user if you only know the reseller password.
Jeff