Some album's first track show up as a different album

Well the title says it. It wasn't so in v10 but certainly seems to be so in v11.

Despite doing everything to ensure all the data across the album (apart from the track numbers) is exactly the same, still the first track in the album is regarded as a separate album.This is not every album, but at least a half dozen I've so far come across. Irritatingly, they are ones I listen to quite often.

The weird thing is that the offending albums have nothing in common. Neither artist, album, genre, ...

I have used iTunes from a couple of years before it was bought by Apple (forgotten what it was called back in the day) and have never come across something like this which I just don't know how to solve.