I have currently upgraded my SS from 2.3.3 to 2.3.7. My TinyMCE editor is striping code from the html - it did however use to work by modifying the cms/code/LeftAndMain.php in SS 2.3.3 as i have done so below.
<br /><a href="http://www.weatherzone.com.au/radar.jsp">weather radar</a>
I have changed the cms/_config.php file by changing:
'valid_elements' => "+a[id|...etc
'valid_elements' => "*",