CallableStatement.getParameterMetaData() throws exception for valid {call ...} statement

Hello,

I just noticed the following:

Using this sample function from the manual:

   CREATE FUNCTION sum_n_product(x int, y int, OUT sum int, OUT prod int) AS $$
   BEGIN
       sum := x + y;
       prod := x * y;
   END;
   $$ LANGUAGE plpgsql;


When calling this through JDBC, the following works without problems:

     cstmt = connection.prepareCall("{call sum_n_product(?,?,?,?)}");
     cstmt.registerOutParameter(3, Types.INTEGER);
     cstmt.registerOutParameter(4, Types.INTEGER);
     cstmt.setInt(1, 2);
     cstmt.setInt(2, 5);
     cstmt.execute();
     int x1 = cstmt.getInt(3);
     int x2 = cstmt.getInt(4);

     System.out.println("x1: " + x1);
     System.out.println("x2: " + x2);

However when calling

      ParameterMetaData meta = cstmt.getParameterMetaData();

after prepareCall() the following exception is thrown:

    org.postgresql.util.PSQLException: ERROR: function sum_n_product(unknown, unknown, unknown, unknown) does not exist
       Hint: No function matches the given name and argument types. You might need to add explicit type casts.
       Position: 15

Casting everything to integer ( "{call sum_n_product(?::int,?::int,?::int,?::int)}" ) produces the same error (except
thatthe parameter list shows integer in the exception message). 

This looks like a bug to me. Why should getParameterMetaData() throw an exception if the call is valid and working?

Driver version is 9.4-1200
Postgres version is 9.4.2
Java version is 1.7.0_55

Regards
Thomas