I solved it this way:
inside DisplayShelf.commitProperties() change the cleanup loop from:

for(i = numChildren-1;i>=0;i–)
{
removeChildAt(numChildren-1);
}

to

for(i = numChildren-1;i>=0;i–)
{
(_children[i] as TiltingPane).remove();
removeChildAt(i);
}

inside TiltingPane add function remove:

public function remove():void
{
if(_content != null)
{
// remove it from our display tree.
removeChild(_content);
// stop listening for update events.
_content.removeEventListener(FlexEvent.UPDATE_COMPLETE,contentUpdateHandler);
}
}