I am having the same problem. My sidebar file is in the root namespace. There are also the playground and wiki namespaces that I want to hide. I have put the following code in the skip_index field in the indexmenu settings:
/(sidebar|playground|wiki)/
Playground and wiki have both stopped displaying (which is good) but sidebar (which again is a file in the root namespace) is still showing. What else do I need to do to hide that file in the nav?
Thanks
Pete