Buttons enabled for node reference extras disappear when validation errors occur in the form

When the form is submitted and there are validation errors, the buttons enabled for node reference extras (search/create and reference, etc.) disappear.

This happens because on validation errors the form is not rebuilt again, hook_form_alter() is not invoked, our after build callback either, which is where we were sending the javascript to the page.

This can be solved using a pre_render callback instead of an after_build callback.

Patch coming...