When you edit any content in "HTML" mode, you are manually overriding the "editor generated" code.  When you insert code, then switch to normal view and make formatting changes, you do run the risk that your manual code will be overwritten as the editor generates new code to display your new text. This is normal for most HTML editors.  

As a rule, you should first edit your content, then second, manually insert/edit the HTML.  This would be the only way to prevent your code from getting reformatted, etc.