I think I found a solution to it. It seems to be something with the HTML5 template I'm using. It started off as the HTML5 boilerplate and only changes that were made were to the paths of the javascript and added some css files too.
Anyhoo... when I convert it from HTML5 to XHTML transitional and then back to HTML5 again, it seems to be fine and works like it should.
The difference is I think either Dreamweaver or DataAssist needs the <html> to be as is and the files I use have <html class='no-js' lang='en'> attached to them. One of the two doesn't like that, I think maybe Dreamweaver as it then will add an additional <html> and keep the <html class='no-js' lang='en'> too.