Well formed HTML causes odd behavior when being saved for 'at the end of BODY' but works fine 'at the end of HEAD' and 'at the beginning of the BODY'.

Steps to reproduce

1. Browse to 'Confluence admin' -> 'custom HTML'
2. click 'edit' and add the following to 'At the end of BODY'

   <form action="http://www.example.com">
   </form>
   

3. Click 'Save"

Notice that upon saving we are redirected to a blank page with 'data:,' in the URL. Please note also that the example form action is rather generic and this failure appears to occur with well formed AJS as well.