Why does rosinstall say my git repo is "not the current branch or commit"?

edit

I cannot update git repositories using rosinstall. I do the first installation by running:

rosinstall ~/ros-test mytest.rosinstall

This completes without error. When I try to update by running:

rosinstall ~/ros-test

... I get:

The version  of repo http://kos.informatik.uni-osnabrueck.de/uos-ros-pkg.git 
requested to be checked out into /tmp/rosinstall-test/uos-ros-pkg is not the 
current branch or commit and cannot be blindly updated in place. 
(d)elete, (a)bort, (b)ackup, (s)kip:

This is the rosinstall file I use:

- other:
    local-name: /opt/ros/diamondback/ros
- other:
    local-name: /opt/ros/diamondback/stacks
- git:
    uri: http://kos.informatik.uni-osnabrueck.de/uos-ros-pkg.git
    local-name: uos-ros-pkg

This only happens with git repositories, svn works just fine. We don't use any black magic such as submodules. I'm using rosinstall version 0.5.16. The repo is public, so you can reproduce the error. Any ideas? Should I file a ticket?