Unable to change placeholder for solid-form-placeholder-text dynamically

Version: 0.16

I can't change the placeholder-xyz of a solid-form-placeholder-text on a solid-form after this one have been generated.
jsbin: https://jsbin.com/nofavuvuri/edit?html,output

Notice that this issue point the placeholder-xyz but in this case it's the same behavior with label-xyz. #733