In Windows 7 / Internet Explorer 8, the Reorder Columns dialog (accessible in a PanelCollection from View > Reorder Columns...) is stretching the full length of the screen. View > Columns > Show More Columns... appears to be having the same issue.
In Windows XP or Windows 7 / Firefox 10, the popup is only about 250px in width.
Using JDeveloper 126.96.36.199.0.
This should be built-in functionality. Any idea why this might be happening?