I noticed a couple visual glitches while using the grouping feature, specifically grouped by album covers.
First glitch is shown in this picture. Selecting albums with SHIFT from top to bottom will also select blank space as if albums were there.

Second glitch is harder to demonstrate. Re-sizing the main window (at least horizontally) results in album covers flashing up for an instant in blank spaces, seemingly at random. Not really a problem, just looks a bit weird.
Edit: It also occurs to me that grouping by decade is currently limited to one direction only, oldest to newest.