While investigating 6482575 (Leak in ImageIcon) I found that we're also leaking AppContexts from WWindowPeer. A static Set named trackedAppContexts was added to fix 6503472 in b15. AppContexts are added to this Set, but never removed.

As with 6482575, I used Chris Oliver's JApplication to reproduce this (along with a small application to show a frame). See his "Poor Man's Multi-VM" blog entry for details:
http://blogs.sun.com/chrisoliver/entry/poor_man%27s_multi-vm