Different ways of extending a class functionality esp. adding getProperty inconsistent

class FooWorksAsMap { // class names the same length as LinkedHashMap to make output pretty
 def getProperty(String foo) { "OK:FooWorksAsMap.$foo" }
}
class BarWorksAsMap {}
class BaxWorksAsMap {}
@Category(BarWorksAsMap) class C {
 def getProperty(String foo) { "OK:BarWorksAsMap.$foo" }
}
BarWorksAsMap.mixin C
BaxWorksAsMap.metaClass.getProperty = { foo -> "OK:BaxWorksAsMap.$foo" }
def maps = [new FooWorksAsMap(), new BarWorksAsMap(), new BaxWorksAsMap(),
           [foo:'OK:LinkedHashMap.foo', class:'OK:LinkedHashMap.class']]
for (def prop in ['foo','class']) {
 for (def m in maps) {
   def op = "${m.getClass().getSimpleName()}.$prop"
   try { println "$op -> " + m."$prop" }
   catch (t) { println "$op -> FAIL:$t" }
 }
}