The -release option throws an exception if a JSR199 implementation uses a JavaFileManager instead of a StandardJavaFileManager:
Error: -release option specified, but the provided JavaFileManager is not a StandardJavaFileManager.

This basically forces any decent JSR199 implementation to use StandardJavaFileManager even if they don't want to.

I wonder if StandardJavaFileManager is really necessary. With the -release option you're basically telling Javac to use the appropriate bootclasspath, so Javac can look there first without having to set it in StandardJavaFileManager and then retrieve it from there again.