placeholder hot working properly

[idphobia]

if the placeholder is defined in the fields, we can do two-way data-binding to change placeholder :
http://jsbin.com/vecarutevu/1/edit?html,js,output

if the placeholder is NOT defined in the fields, anything change to fields.to.placeholder is not updating the form.
but the labels works if its not pre-defiend in the fields
http://jsbin.com/nobepiheki/1/edit?html,js,output