I’m trying to write some html in the “Html” tab of TinyMCE while editing my page and the editor keeps modifying my markup when I save the page. For example it removes my <br> tags and replaces my <i> tags with <em>.
Is there any place I can turn this “AUto Correct” feature completely off?
This Plugin will fix your Problem: http://wordpress.org/extend/plugins/preserved-html-editor-markup/
It disables “wpautop” that is responsible for the “Auto Correction”.
First you need to know that there are two levels of correction.
In your case it looks as of your tinymce configuration is not set propperly.
Please check your tinymce configuration for the settings valid_elements and valid_children.
WordPress will edit your html by converting line breaks to paragraphs etc. If you want to add html through the text editor and not have it get broken later use a plugin like the RAW HTML plugin:
http://wordpress.org/extend/plugins/raw-html/