This bug is observed on all the platforms and on GTK LAF.
The tab traversal path in GTK LAF is different from traversal path in Windows and Linux LAF in SwingSet2.

Setps to reproduce:
1. Select Table demo.
2. Take the focus on "Reordering allowed" checkbox.
3. Now tab to "Intercell spacing " slider.
4. The next tab takes focus to "Selection Mode" combo.
5. Now change the LAF to GTK.
6. Now repeat steps 2 and 3.
7. Next tab takes the focus to "Column Selection" checkbox and not to "Selection Mode" combo as in metal or XP or Motif LAF.
8. Now traverse to "Selection Mode" combo.
9. Note that the combo has no selection border.