Version info

Angular: 2.4.7
Firebase: 3.6.9
AngularFire: 2.0.0-beta.7
Other (e.g. Ionic/Cordova, Node, browser, operating system): N/A

How to reproduce these conditions

Failing test unit, Plunkr, or JSFiddle demonstrating the problem

There is a plunk here.

Steps to set up and reproduce

Open the above plunk and then:

• Open the Dev Tools and go to the Network tab.
• Select WS or All to observe the WebSocket traffic.
• Run the plunk.
• There will be an entry of about 7557 bytes which is the initial content written to the database.
• That entry will be followed by two of about 7550 bytes and those entries are the content thats read from the database.

The problem is caused by on('child_added', ...) not being called until after the on('value') promise has resolved.

Expected behavior

When subscribing to a FirebaseListObservable that has content that exists in the database, a single copy of the content should be retrieved across the network.

Actual behavior

Two copies of the content are retrieved across the network.