Object.seal() behavior is not correct

[RuralHunter]

According to the specification, the values of present properties of a sealed object can be changed as long as they are writable. The code below runs correctly in real browsers but fails in rhino with EcmaError: TypeError: Cannot add properties to this object because extensible is false.

fun=function() 
{ 
        "use strict"; 
        var r = {}; 
        Object.defineProperties(r, 
        { 
                a: { writable: true, value: 'aaa' } 
        }); 
        r.a='abefore'; 
        Object.seal(r); 
        r.a='aafter'; 
}; 
fun();