sometimes we only small test runs with only some parts of the catalog. In a such an test plan we mentioned that sub catalogs without test cases are displayed, too. This leads to an messed up test plan. I think it wouldn't hurt someone when this sub catalogs aren't visible.
Filed an enhancement request: https://trac-hacks.org/ticket/10805
I'm working on some enhancements during these days.
Expect a new release to be available soon :D