There are different rendering issues in GTK native LAF that were gathered here. They exist in build 62. They should be fixed to make GTK native LAF looking like native applications.
1) JTableHeader cells should be painted like buttons.
2) Background for popup menues should be painted correctly. SmokeBlue theme shouldn't throw NPE when popup menu is opened
3) ArrowButton images for JSpinner and JScrollBar should be cached separately in CachingPainter
4) ArrowButtons in JSpinner, JScrollBar, JComboBox, JTableHeader should have correct sizes.

To test the behaviour use the attached test.