The sub connections can't be deleted when the parent connection was deleted

1.Create a XML-to-XML mapping
2.Link the source collection node to target collection node.
3.link the sub node of source collection node to target sub node of collection node.
4.Save
5.Open it again and delete the parent connection ( the line between the source/target collection node)

The sub connection can't be deleted.

Please take a look the flash :
http://screencast.com/t/IbQvPoBvQ