I can't install releases of packages from devpi other than the latest release.

All releases show up in the listening:
$ devpi list package

Installing version 0.6.1 goes without problem, but instaling an older release is not possible:

$ pip install --upgrade --trusted-host devpi.corporate.com --find-links http://devpi.corporate.com/dev --no-index package==0.6.0
Ignoring indexes: https://pypi.python.org/simple
Collecting package==0.6.0
Could not find a version that satisfies the requirement package==0.6.0 (from versions: 0.6.1)
No matching distribution found for package==0.6.0

Is their something I'm missing?