Changing an async belongsTo association does not load unfetched record.

[Fixes #1567]
It does the trick, TDD approved ;-)
 
![screen shot 2014-08-04 at 11 35 50 am](https://cloud.githubusercontent.com/assets/743977/3801628/41d02188-1c06-11e4-9190-233e31b7212d.png)