I do agree with you that that's a bit weird, not sure yet why it would do that.
This might not be relevant to your original post, but I did find this interesting and I've never noticed it before.
When I'm using the Album and Tracks view and click on the artwork, MB selects all the files on that album. If I then right click, the option to "Auto-Tag by track" is visible in the right click menu.
However, when I'm using the Album Cover view and repeat the same process as described above, "Auto-Tag by track" is no longer available/visible in the right click menu. Still, if I choose the Edit option in the right click menu, all the files of that album will be edited which of course means that all the tracks are selected as expected. Basically, right clicking on the artwork in the Album Cover view produces a right click menu that differs from the one in the Album and Tracks view.
As mentioned, this probably doesn't have anything to do with your issue. Just putting it out there that there might be some behavior discrepancies between the different view options.