Grrrr very frustrating. When you add pieces of HTML code to pages and add code tags in the HTML view when you switch back the tags have disappeared. To get around this you need to encode the tags using HTML encoding.

The &gt; and &lt; are character entity references for the > and < character in HTML. It is not possible to use the less than (<) or greater than (>) signs in html, because the browser will mix them with tags. To use these characters you can use entity names (&gt;) and entity numbers(<).

Just do a search & replace to change the < and > then to &gt; and &lt;.