enabling attachement messes comment submission

Steps to reproduce:

1. In Drupal 6.4, enable Comment core module
2. Enable Attachments module and its dependencies
3. On a published node, enter a comment and request a preview
4. Attempt to save the comment

Erroneous behaviour: Despite of being enabled (in HTML sense) and pressable, the "Save" button seems to have no effect. Pressing it doesn't submit the comment form.

The notification message "ATTENTION: your comment is NOT YET posted - please click the post button to confirm your post" isn't displayed, and occasionally, the preview page won't complete downloading/rendering unless the form is resubmitted!

Attempting to save a comment without previewing it completes successfully with no problem.

Unloading Attachments module and reloading the commenting form's page clears the problem.

Hint: The problem seems to manifest firstly in the comment authoring page, since enabling or disabling Attachments module then returning to the commenting page from the browser's cache doesn't change the result of submitting a comment as described above. In order to see the effect of enabling/disabling the module the page containing the comment authoring form must be reloaded.