This was done on purpose so you could see that the specific album is released as "John Lennon & Yoko Ono" and not just "John Lennon".
You can disable this behavior. Right-click tree view and select Customize View. Switch to Options tab. You will see this format string in first box:
Remove the first part in curly braces and press OK. Your new format string should look like this:Code:{%b :: }%T{ (%Y)}
(Technical explanation: %b expands to full artist name if it's collaboration album, or expands to empty string if it's simple artist album. If you remove %b, artist will never show up.)Code:%T{ (%Y)}