is it reproducible and if so what steps did you take
Very much so.
Open MB > click Auto-DJ (under Playlists) in left sidebar.
This is before I enter any criteria, and even when I do. I -think- it's the Auto-DJ preview.
I have the "playing tracks" panel at the bottom of the main panel. If I remove that, then the partial headers are visible. So it looks like the playing tracks panel needs to be resized.
With playing tracks panel at bottom:

With playing tracks panel removed from bottom:
