When HTML code dissappears after editing a page

Why do various html code dissapear after you make an edit to a page/post via the Visual tab. And more importantly, how can I ensure this doesn’t continue to happen?

I have had problems with this in the past, wordpress does some auto formatting when you save it. I cant remember what solution I used to fix it but I have found some solution for you to try

It looks like they work with wordpress 2 not sure about 3.

One thing that you should do is deactivate the visual editor as I remember that making life much better. Just use the code view. You should be able to deactivate the visual editor in ‘Users Personal Options’.