Youtube does not work ok (strange characters in login name)

A problem with my fathers tv:
Logging in Youtube via de tv works fine, but the display login name is nog the correct one. Strange characters are shown (like: ddd883jdiiii, or something like that). Using a wrong password to login doens't work, so the login procedure should be ok then... When accessing the favorites it continuously shows "Loading...".

When I use my own Youtube account it does work fine. The username is shown correctly and I can access and play my favorites with nog problem...

Any idea what the problem (and solution) could be?

Regards....

May be your father given any hind of user name and password.