Nimbus - JOptionPane's showConfirmDialog()renders the Yes, No, Cancel buttons differently. On Win XP the order should be Yes, No and Cancel starting from the left. Nimbus renders Cancel, No and Yes. And for just Yes, No dialogs.. No is rendered on the left side. The end user of an application had to change where they used to click regularly for doing the same action. This needs a lot of change in the user interation with the app. ending in clicking on the wrong buttons. This issue is also been reported on the http://forums.java.net/jive/thread.jspa?threadID=31434
So the order of buttons should match the native platform.
Please see the attached images for more details.