Problem: The method "listLatestUpgradablePackages" returns, according to the API documentation, an array with the variables. One of the variables listed is "package_name"; however, the API is actually returning "name" instead. The API documentation should be updated to reflect the correct return parameter name.
Fix submitted in to git to change doc from 'package_name' to 'name'. git commit: 052bd04b8ad059e7a79bb93ecd81c00799ceb00e
Verified, docs now say "name" at: http://www.redhat.com/spacewalk/documentation/api/0.3/handlers/SystemHandler.html#listLatestUpgradablePackages
Spacewalk has been released for some time.