The build is tested with JDK 1.7. As JDK 1.8 is not even final yet I have not done any testing with it.

It would seem that the problem is the definition of the generateMainLoggingClasses task, and specifically its declaration that source = sourceSets.main.originalJavaSrcDirs. Note sure why this would fail on JDK 1.8 but not on JDK 1.7. Something obviously changed there in regards to -proc:only handling..