Ok, its as I expected, but the behavior is peculiar, probably having something to do with when MC calculates the [Album Type] and [Complete Album] fields.
It is related to the [Disc #] field.
When [Disc #] is the same for all the tracks, MC will use the criteria you've noted.
When there is a gap between the [Disc #] field for the tracks, MC appears to be using a slightly different criteria.
It is not sufficient to just delete the [Disc #] values, or set them all the same, as MC won't re-calculate the [Album Type] / [Complete Album] fields, so the album will remain incomplete. However, you can force the matter by changing any tracks album name temporarily, and then changing it back. MC will then shortly thereafter recalculate [Album Type] and [Complete Album].
@Matt - since [Album Type] and [Complete Album] rely on the fields [Album], [Track #], [Disc #], [Filename (path)], and [Duration], perhaps those two calculated fields should be re-evaluated and updated whenever any of those field's values change.