Product Version = NetBeans IDE Dev (Build 100825-ba4898edabae)
Operating System = Linux version 2.6.33.8-149.fc13.x86_64 running on amd64
Java; VM; Vendor = 1.6.0_20
Runtime = Java HotSpot(TM) 64-Bit Server VM 16.3-b01

The problem is reproducible for 6.8 and version built from trunk.

The code itself runs fine on Grails 1.3.4.

Code snippet from Grails application:

    private def getJSONConfig() {
        JsonConfig jsonConfig = new JsonConfig();
        jsonConfig.setJsonPropertyFilter(
            new PropertyFilter() {
>> Message goes here.
                public boolean apply(Object source, String name, Object value) {
                    return name.equals("id") || name.equals("version");
                }
            }
        );
        return jsonConfig;
    }