WordPress is Stripping HTML!

It depends on what the HTML is. Sometimes wordpress will strip out dangerous code (iframe) or bad code, for example:

<div>
<h3>
Hello World, this is bad code!
</div>
</h3>

If you want specifics you’ll have to copy/paste the code you’re trying to insert.

You could use something like this: Embed Iframe which uses a shortcode to replace the embed code.

More info on how that works here: http://wpgarage.com/tips/stop-wordpress-stripping-iframe-html/

Hope this helps!