Aha, I should have guessed from the hosting company's name you mentioned that this would be an ASP.NET site. That type of CMS (content management system, i.e. your site builder) makes every page into one, big, full-page Web form which it uses to manage your site content and layout. Since forms can't be nested one inside another, this causes problems with our button codes for Variants/Variations (which uses a form to submit the Comments to the cart in your case), and those button codes in turn may cause problems with the ASP.NET system.
The first button doesn't work right because it's activating the form action of the full-page ASP.NET form, rather than the button code's own form action. The other buttons work fine because the </form> tag at the end of the first button's code ends the ASP.NET full-page form prematurely (rather than where it should end, at the bottom of the page). However, this may be causing problems with your ASP.NET system, which may explain the malformed HTML I found in your page (notably, an entire extra HEAD section plus extra <body>, </body>, and </html> tags in the middle of the page).
If you absolutely need to have these Comment fields, you may need to contact your hosting company's support team to inquire whether our ready-made button codes using forms could be inserted in your page, and if so, how they would recommend that should be accomplished.