form textfield name -value changed and does not validate any more
It all happens in drupal_validate_form(). 


  Validates user-submitted form data in the $form_state array.


If I could offer some advice - have a re-think. Changing the name attribute of form elements, especially on those that are part of field widget forms, is a good way to get unexpected results. The name on an input is completely irrelevant to the page, so changing it doesn't actually get you anything. If you're trying to change it so you can target the elements using JS, for example, I'd advise changing your JS code rather than the form markup. Trust me when I say it will be easier.

The only valid situation I know of to override the name of an element is when you need to provide multiple submit buttons on a single form that carry out the same action, but in a different context.