I have noticed that WP strips a lot of code out of pages. I’m having so many problems with it stripping all <p> and </p> tags that I’m about ready to redo my wife’s site back to HTML. I don’t know what’s going on with WP, but I’m getting very discouraged with it.
It is very simple: the wysiwyg (visual) editor is for code illiterates – for those that do NOT use any html code in their posts ever.
If you know code – your should disable (admin > Users > Your profile) the visaul monster.
After that you can use any code in your posts/Pages and WP will never alter it.