A link that stands out is http://www.devdaily.com/blog/post/jfc-swing/handling-main-mac-menu-in-swing-application/ however the menu bar under Mac OS X displays as the packag
If you are launching multiple JFrames and you use the mac menu, then one of the JFrames could be replacing the JFrame you want with one that has a different menu structure. I'm not sure if you can share one JMenuBar for multiple JFrames, but you could just make an application wide menubar that all the frames instantiate.