Suppose we have a proxy that uses BaseProxyHandler::set, and the proxy's getPropertyDescriptor and getOwnPropertyDescriptor methods behave as if x were an inherited value property. In emulation of the ordinary object internal methods' behavior, assigning to the proxy's x property should ask the proxy's handlers to define a new writable, enumerable, and configurable own property x, with the newly assigned value. However, the present code in BaseProxyHandler::set makes the new own property inherit all the attributes (including the value!) of the property it shadows. Bug 738244 fixes the way BaseProxyHandler::set tosses the newly assigned value, but the inheritance of the shadowed property's other attributes is still wrong, and should be fixed.

Is this still a problem?

This applies to old-style proxies; the test from bug 738244 does: Proxy.create(handlers).x = 43; but Proxy.create doesn't even exist any more.