There are differences in redering some controls in Mustang and Tiger.
The differences are described at http://www.ffnn.nl/pages/articles/java/java-2-se-6.0-aesthetics-preview.php
This bug covers two of them:
1) combobox arrow button is rendered correctly on the 1.5, while Mustang draws a boxy and flat arrow.
2) JSlider doesn't have the center indicator anymore.

To reproduce the bug run SwingSet on Mustang and Tiger and compare comboboxes and sliders there.