Because JDK8 now ships with jfxrt.jar in the jre/lib/ext directory, that file will be used in preference to classes in other jars on the classpath. This means that when building the FX runtime, we will be compiling source code from our current repository, but getting any dependent class files in other modules from whatever version of those classes is in the installed JDK8 build being used. If there are any interface changes, we will fail to compile.