Afair, this was a known issue which was fixed in the later versions.
(CapeDwarf version on OpenShift is pretty old ...)
luksa can tell you more.
Perhaps this could be a workaround:
If you can work with dev type of login,
you can remove the system property "com.google.appengine.runtime.environment" we somewhere set in OpenShift + CD script.
(this property needs to be set to "Development")
Can you post the stacktrace or any other info?