When SwingSet2 demo is started and LookAndFeel is changed to GTK LnF, the frame size is clipped and does not show JTable,Tooltip and JTree demo. The SwingSet2 frame needs to be dragged & resized to see these 3 demos. Probably the minimum size is not taking into account the demo icon/name change when GTK L&F is loaded.

Attached screenshot shows the problem of not showing JTable,Tooltip and JTree demo.
It happens for GTK2 too but there only JTree demo is partially shown. But in GTK3, JTable,Tooltip and JTree are not shown.