asudoh/dojox_mvc — comment on commit 5150504c50b1b08c8196eb2192e29a5fb10b379f
File: Bind.js line 152
By asudoh:

The original logic is in _updateBinding() function in _DataBindingMixin.js:

var val = binding.get("value");
if(val != null){
this.set("value", val);
}

I have a similar guess, too... Though it sounds natural to copy the observed value no matter what the value is, changing the behavior there may break some applications.