A DESCRIPTION OF THE PROBLEM :
In the following example, I try to assign function references and a lambda to generic functional interfaces.

In the first example, I successfully assign a reference of bar to Function0 generic functional interface.
In the second example, both type arguments include wildcards with extends, and I managed to assign a lambda.
In the last example, I tried to assign a reference of foo to Function1 (which is similar to the previous lambda), but the compiler reports an error message. More specifically, it reports: "incompatible types: Number cannot be converted to Short", if I replace the first type argument to ? extends Short, the program compiles.

It looks to me that there is an inconsistency between handling lambdas and function references. Is there something that I am missing here?

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
javac Test.java

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Compile successfully
ACTUAL -
Test.java:15: error: incompatible types: invalid method reference
    Function1<? extends Number, ? extends Number> f2 = Test::foo; // does not work
                                                       ^
    incompatible types: Number cannot be converted to Short
1 error

---------- BEGIN SOURCE ----------
class Test {
  public static Short foo(Short x) {
      return x;
  }

  public static Short bar() {
      Short x = 1;
      return x;
  }

  public static void main(String[] args) {
    Function0<? extends Number> f = Test::bar;

    Function1<? extends Number, ? extends Number> f1 = (Short x) -> x; // works
    Function1<? extends Number, ? extends Number> f2 = Test::foo; // does not work
  }
}

interface Function0<R> {
  public R apply();
}

interface Function1<P, R> {
  public R apply(P x);
}

  public static Short bar() {
      Short x = 1;
      return x;
  }

  public static void main(String[] args) {
    Function0<? extends Number> f = Test::bar;

    Function1<? extends Number, ? extends Number> f1 = (Short x) -> x; // works
    Function1<? extends Short, ? extends Number> f2 = Test::foo; // does not work
  }
}

interface Function0<R> {
  public R apply();
}

interface Function1<P, R> {
  public R apply(P x);
}

---------- END SOURCE ----------

FREQUENCY : always