W3C validator doesn't like this html:
<a id='gf_$form_id' name='gf_$form_id' class='gform_anchor' ></a>
It is displayed when form is ajax or has_pages.
W3C says: "The name attribute is obsolete. Consider putting an id attribute on the nearest container instead."
The html could simply be replaced by:
<a id='gf_$form_id' class='gform_anchor' ></a>
Unfortunately, there is no filter to just strip this attribute. I could remove the anchor wih the "gform_confirmation_anchor" filter but it would cause problems to ajax forms.
I hope you can can fix that in the next updates.