The root cause is that libwnck (the window list) is providing a size hint based on the desired width of the buttons * the number of columns (based on 25 characters visible), and gnome-panel using that hint to determine the vertical size of the switcher.
This is a duplicate of 152838.
The root cause is that libwnck (the window list) is providing a size hint based on the desired width of the buttons * the number of columns (based on 25 characters visible), and gnome-panel using that hint to determine the vertical size of the switcher.