Grails grails.project.target.level config has no effect? - grails

Question

How do I compile my groovy source code into java 1.8 bytecode?
I'm using Grails 2.5.4, Java 1.8.0_74
I might be missing something obvious here, but the below settings in Grails BuildConfig.groovy don't seem to affect the Java bytecode being generated for Groovy source files.
Major version 49=Java 1.5, and 52=Java 1.8 (cite: how to check the jdk version used to compile a .class file)
grails.project.target.level = 1.8
grails.project.source.level = 1.8
Then to check bytecode version:
$ javap -verbose target/classes/MyGroovy.class | grep major
(standard input):7: major version: 49
$ javap -verbose target/classes/MyJava.class | grep major
(standard input):7: major version: 52
$ javap -verbose target/classes/UrlMappings.class | grep major
(standard input):7: major version: 49
$ javap -verbose target/classes/BootStrap.class | grep major
(standard input):7: major version: 49
So based on the above results, it seems that the target.level=bla configuration does affect Java source code, but not Groovy?
My test setup:
Vanilla grails 2.5.4 app: 'grails create-app foo'
Added one java source file, and one groovy. Placed in foo/src/*
Modified BuildConfig.groovy and set target/source levels to '1.8' instead of the default '1.6'
Those are all the steps. Totally simple.
My source code:
class MyJava {
String name;
int age;
public static String foo() { return "java!"; }
}
And...
class MyGroovy {
def name
def age
static foo() { 'groovy!' }
}