I encountered the following exception while trying to refactor a package name, when the refactoring was in its data gathering phase.

I had previously refactored a package in a different project that this one depends on.  This worked successfully, but the class metadata cache was clearly 
screwed up - I refactored
org.netbeans.libs.wicketmodels to org.wicketstuff.quickmodels
in the attached project wicket_persistencefacade_models
then I refactored the same package in test sources (shouldn't this be automatic, the way IntelliJ does it?)
then I moved to the attached project persistencefacade and refactored 
org.netbeans.libs.persistencefacade into org.wicketstuff.persistence
and in the data gathering phase the following exception was thrown

Generally package refactoring seems to be pretty unstable.  Build 071115.

java.lang.IllegalArgumentException: All children must have the same parent: Users/tim/space/persistence/TopicAuction/persistencefacade/src/org/
wicketstuff/persistence vs. Users/tim/space/persistence/TopicAuction/persistencefacade/src/org/netbeans/libs/persistencefacade
	at org.openide.filesystems.Ordering.getOrder(Ordering.java:109)
	at org.openide.filesystems.FileUtil.getOrder(FileUtil.java:1604)
	at org.openide.loaders.FolderList.carefullySort(FolderList.java:585)
	at org.openide.loaders.FolderList.createBoth(FolderList.java:827)
	at org.openide.loaders.FolderList.access$700(FolderList.java:74)
	at org.openide.loaders.FolderList$2.run(FolderList.java:366)
	at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:561)
[catch] at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:986)