Script plugin non-instance configuration fails

[MartinMulder]

I have a script plugin (workflow node step) and try to use "Project" or "Framework" scoped config (with RD 2.4.2).
The plugin is listed in the "List plugins", and if selected I get:

infraconfigurations path:
Path to infra-configurations SVN checkout
configure project: project.plugin.WorkflowNodeStep.mo-esb-package.icpath=value

Plugin provider config:

     - name: mo-esb-package
       service: WorkflowNodeStep
       title: ESB Packager
       description: Package an ESB node
       plugin-type: script
       script-interpreter: /bin/bash
       script-file: esb-node-package.sh
       config:
         - type: String
           name: icpath
           title: infraconfigurations path
           required: true
           description: Path to infra-configurations SVN checkout
           scope: ProjectOnly

project.properties line:

project.plugin.WorkflowNodeStep.mo-esb-package.icpath=/tmp

When I add the "ESB Packager" to a workflow, and try to save it, I see an error in the service.log:

2015-02-27 13:31:14,085 ERROR WorkflowController - Plugin configuration was not valid

[gschueler]

workaround would be to remove required: true from the property config