help needed: widgEditor very slow with IE in some conditions

I wanted to make a pop-up like window which displays widgEditor to post some content on a site. I used a div with negative z-index that become positive when users click on a link. The default textarea content has to be different if the user wants to create a new post or update an old one, so the textarea is created with AJAX every time a user clicks on the link. With Firefox everything works perfectly, but with Internet Explorer widgEditor is very slow, so users write and must wait long seconds before their words appear on the wysiwyg editor. Can anyone help me sorting out this problem? It's very important! If you want to understand exactly what's the problem, you can look at an example page here http://www.lucaongaro.eu/test/test.html (click on the link "write something" and widgEditor will appear).
Thank you