Open Radar

 
When I implement KVO, the KVO notifications will fire extra times under this situation: add 2 or more of the same observers to the same keyPath without context (nil) and 1 of the depending key is a keyPath of member property. When the depending keyPath is changed, the number of notifications being fire will be a multiplication of the number of said observers.

Steps to Reproduce:
1. Create an NSObject class called Foo with these member properties:
dynamic var fullName : String (can be computed or stored)
dynamic var firstName : String = "Foo"
dynamic var bar : Bar = Bar()

2. Create an NSObject class called Bar with these member properties:
dynamic var lastName : String = "Bar"

3. Register depending keyPaths ["firstName", "bar.lastName"] to key "fullName" of Foo

4. Now in the init of Foo, add observers as follow:

self.addObserver(self, forKeyPath: "fullName", options: NSKeyValueObservingOptions.new, context: nil)

self.addObserver(self, forKeyPath: "fullName", options: NSKeyValueObservingOptions.new, context: nil)

5. Now trigger the notification by changing the value of "bar.lastName" to "Baz". 

Expected Results:
There should be 2 notifications sent.

Actual Results:
There are 4 notification sent.

Version:
Xcode Version 8.1 (8B62)