Rendering vertical tabs inside vertical tabs

This is what I get, so far (see the attached screenshot).

After the shown fieldset, there are again the form fields added by Nodewords, rendered from Vertical tabs.

It seems I have problems on attaching the image (it is just 70 KB).I will then describe what I get.
The module Nodewords add a fieldset Meta tags to some forms. In the case of the node edit form, what I get is to see all the form fields, including the one not related to the module inside Meta tags; at the bottom of the form, but before the buttons, I see the form fields added by Nodewords, still rendered by Vertical tabs.

This seems a particular case, but it could happen on every form where Nodewords add its own form fields.
I guess I should add the support for Vertical tabs only in the forms created by Nodewords.

Is this a known issue?

I am sorry for the screenshot; it seems that sometimes I cannot add attachments.
This time I was able to add it.

What it is not visible in the screenshot is what I was talking of in the comment #2; the form fields the module adds are duplicated at the bottom of the form, right before the buttons.