1) Open SwingSet2
2) Change to Windows L&F
3) Go to combo box demo.
4) Now click in middle of the combo box(Not on the down arrow button, but on middle) using left mouse button.
5) Note when you click the arrow button remain unchanged.
6) Now open any native application which have combo box(which is not editable).
7) Say we use. Right click on desktop and select Display Properties.
8) Now go to Themes tab, now repeat step 4 for this native combo box.
9) Notice that here when you click on middle of Combobox, the down arrow button shows press effect which is not case with java combobox.

Bug can be reproduced in Win2k too.
This bug exist in Tiger also.