This is reproducible on Solaris and Linux on mustang b53. This is not reproducible on b53 AWT PIT build.
The drop box of a JComboBox does not stay when clicked. It drops down and disappears.
The testcase is attached.
To execute it, extract the tar file, cd to 'swing' directory, set JAVA_HOME and run the script.
Click on the JComboBox. If the drop down does not stay, bug is reproduced.