Can't write to The applyStroke attribute

I have several lines of simple code like this:

     var myComp = app.project.activeItem;

     var myLayer = myComp.layer(1);

     myLayer.sourceText.value.applyStroke = true;

     alert(myLayer.sourceText.value.applyStroke);

However, the applyStroke doesn't work properly, I can read its value, but can't write it. According to the official scripting guide, it's read/write.

But the 3rd line just doesn't work! I wonder why! Is this a bug? !

Hope I've made myself clear.