Aggregate value not updating when model changing

[cyrilgandon]

Plunkr : http://plnkr.co/edit/fOPGOvfpE1EWmvMPBkSE

Click on Increase button to change values.

Expected : aggregate value in footer should update as the values are changing.

[PaulL1]

I think this has the same root cause as #3442, and therefore probably the same solution.