Why should Media Center ignore Album gain? Or do you mean ignore 'ReplayGain Album gain', but use R128 Album gain?
Media Center 19 now uses analysis of the playlist to determine whether "track gain" or "album gain" should be used, and "album gain" is now dynamic rather than a fixed value.
So if you have a playlist which is full of random tracks, it will use "track gain" for volume leveling. (adjusting each track to be played at approximately the same volume level)
But if you have a playlist made up of tracks from the same album played back-to-back, it will play them using a calculated "album gain" value - the average gain of those files.
This adjusts the overall volume of the album to match the volume level of other tracks, but retains the album dynamics. (e.g. track 7 is supposed to be quieter than the rest, or track 3 is meant to be louder etc.)
Album gain is no longer a fixed value, but based on the tracks which are actually in the playlist together.
So if you play an album but remove the bonus tracks from the playlist, the album gain might be a different value than if they were included.
This means that you can have tracks from the same album played together inside a mixed playlist, and those tracks will still retain the album dynamics (whether they were supposed to be louder or quieter than each other) but should be a better fit to the normalized level of the playlist than if you used the old method of calculating album gain, which produced a fixed adjustment rather than one based on which tracks are actually being played.