There is a bug with most specific and default methods when two signatures are merged from a interface as a result of generic specialization:

class Test {
    public void testMergeAbstract(DA<String> da) {
        da.m("");
    }

    public void testMergeInterface(DI<String> di) {
        di.m("");
    }

    abstract class DA<T> {
      abstract int m(T arg);
      int m(String arg) { return 42; }
    }

    interface DI<T> {
      int m(T arg);
      default int m(String arg) { return 42; }
    }
}


This gives:

Test.java:234: error: reference to m is ambiguous
        di.m("");
          ^
  both method m(T) in DI and method m(String) in DI match
  where T is a type-variable:
    T extends Object declared in interface DI
1 error

Note that the dual case with abstract classes work just fine.