As I already told you, I do not have a real usage of the plugin. It came into my root build.gradle because there a plans to integrate the gradle build into Eclipse and make usage of Eclipse WTP.
Maybe the apply-plugin, where I put this plugin, should not be in the root build script. There I had:
subprojects { subProject ->
apply from: '../libraries.gradle'
apply plugin: 'java'
apply plugin: 'eclipse'
//
um Eclipse-Projekte zu generieren
apply plugin: 'eclipse-wtp'
(...)
Anyway, in the momemt I do not care on this plugin, so I commented it out.