multiple propertyDidChange triggering observers only once

[patricklx]

See this jsbin:
http://jsbin.com/mipibunusu/1/edit?html,js,console,output
This jsbin mimics the behaviour of reduce computed and ember data.
In the console output you can see the counter increasing, but then only decreases once.

I encountered this issue while working on #9492 .

reduce computed counts the number of willChange and didChange. see this line

However, sometimes it did not receive the didChange event, which then causes it not to flush the changes. Especially when ember data is used.

[rwjblue]

I did a little digging on this one. Brain dump follows:

Inside ComputedPropertyPrototype.didChange we call removeDependentKeys which calls unwatch here. After that, the data key is marked as not being watched causing the guard in propertyDidChange here to do an early return.

This seems like expected (but bizarre) behavior, but I'll let others that are more familiar with the metal caching strategies chime in to confirm.

[rwjblue]

reduce computed has been removed (as have before observers) so I believe this issue is likely resolved.