The platformlabelers' labels don't seem to "work" until you go into a Node and configure it and save (you don't have to change anything).

To recreate:

• Install the plugin
• Create a job restricted to nodes with expression like "CentOS&&firefox&&jruby" (assuming you have a node like that)
• Restart Jenkins
• build the job

Notice how it says that no nodes exist for "CentOS&&firefox&&jruby". You can click on it and it shows no nodes matching that.

To fix:

• Go to a node with CentOS as a label
• configure it
• save it (no changes needed)

Notice how the job finds the appropriate node.