a Matrix job M is set with combinations parameter
it uses parameterized build trigger to run job J as a downstream
rendering job J "parameters" page fails, as [value page](https://github.com/jenkinsci/matrix-combinations-plugin/blob/master/src/main/resources/hudson/plugins/matrix_configuration_parameter/MatrixCombinationsParameterValue/value.groovy) expect the current project to be the MatrixProject which defined the parameter.
MatrixCombinationsParameterValue contains all necessary informations (confs and values) so there's no need to rely on the MatrixProject to render. Same for [rebuild](https://github.com/jenkinsci/matrix-combinations-plugin/blob/master/src/main/resources/hudson/plugins/matrix_configuration_parameter/MatrixCombinationsParameterValue/rebuild.groovy)