Captcha error

This was described first here and it may be related and/or duplicate of #572772: Spam filter (mollom?) on g.d.o prevents posting and provides no captcha or validation.

When I try to attach a file to an existing comment it fails (with a JSON response) due to some CAPTCHA (Mollom) issues.

Steps to reproduce:

1. On http://groups.drupal.org I click edit on an existing comment (it is my comment)
2. I choose (Browse) a file to attach from my computer - under "File attachments"
3. I hit the "Attach" button
4. The file is attached but I got a status message inside "File attachments" fieldset:
   We're sorry, but the spam filter thinks your submission could be spam. Please complete the CAPTCHA.

   ...but there's no visible CAPTCHA

5. I hit form's "Save" button and I get in the page status messages area:
   We're sorry, but the spam filter thinks your submission could be spam. Please complete the CAPTCHA.

   ...plus the CAPTCHA in the bottom of the page and only the "Preview" button.

6. I enter the CAPTCHA and hit "Preview" and I got a JSON response... :-(
   {"status":true,"data":"\x3cdiv class=\"messages error\"\x3e\nWe're sorry, but the spam filter thinks your submission could be spam. Please complete the CAPTCHA.\x3c\/div\x3e\n\x3cdiv class=\"form-item\" id=\"edit-upload-1-wrapper\"\x3e\n \x3clabel for=\"edit-upload-1\"\x3eAttach new file: \x3c\/label\x3e\n \x3cinput type=\"file\" name=\"files[upload]\" class=\"form-file\" id=\"edit-upload-1\" size=\"40\" \/\x3e\n\n \x3cdiv class=\"description\"\x3eThe maximum upload size is \x3cem\x3e1 MB\x3c\/em\x3e. Only files with the following extensions may be uploaded: \x3cem\x3ejpg jpeg gif png txt html doc xls pdf ppt pps odt ods odp psd csv\x3c\/em\x3e. \x3c\/div\x3e\n\x3c\/div\x3e\n\x3cinput type=\"submit\" name=\"attach\" id=\"edit-attach-1\" value=\"Attach\" class=\"form-submit\" \/\x3e\n"}

Something is wrong with Drupal Groups CAPTCHA/Mollom processing...