Blog bug in Opera browser

I have a blog (running on the Wordpress): [login to view URL] And there is one bug under Opera browser. If you will choose any article. As example: [login to view URL] And click on "Reply to this comment" under any comment right column will "jump" down. And if you click "Click here to cancel reply". Reply field will become wide. That's happening only under Opera. Internet Explorer and Firefox are fine. I am looking for somebody, who can look into HTML + JavaScript to find out what is the problem. I need to know what is the problem in HTML or JavaScript and how to fix it. If this code is generated by PHP (Wordpress) I will take care about this part by myself. So, don't need you to touch any PHP code.