Yes, this is "expected" (understand: the code in the product reflects this behavior, and of course there is a bug):
the code to manage the attribute "disabled" in the StartMenu is there and is working. What is not working is the code which applies the attribute at the widget creation. So when creating the StartMenu as tree, we don't apply the attribute, but later on when you modify the attribute, it is applyed.
So the workaround is expected to work - you can use it safely (if there is no side effect) until the fixed version comes out.