The dispose method of the sun.awt.AppContext never remove the appContext from the static hashtable of AppContext instances. The current code is

// Next, we remove this and all subThreadGroups from threadGroup2appContext
int numSubGroups = this.threadGroup.activeGroupCount();
if (numSubGroups > 0) {
ThreadGroup [] subGroups = new ThreadGroup[numSubGroups];
numSubGroups = this.threadGroup.enumerate(subGroups);
for (int subGroup = 0; subGroup < numSubGroups; subGroup++) {
threadGroup2appContext.remove(subGroups[subGroup]);
}
}
It should be :

// Next, we remove this and all subThreadGroups from threadGroup2appContext
int numSubGroups = this.threadGroup.activeGroupCount();
if (numSubGroups > 0) {
ThreadGroup [] subGroups = new ThreadGroup[numSubGroups];
numSubGroups = this.threadGroup.enumerate(subGroups);
for (int subGroup = 0; subGroup < numSubGroups; subGroup++) {
threadGroup2appContext.remove(subGroups[subGroup]);
}
}
threadGroup2appContext.remove(threadGroup);

This creates memory leaks in the plug-in and swing run-time.