Resource types

Hello
I made a custom form to insert/edit value in a custom table. I have done that with the formslib.php function creating a xxxx_form.php file following the examples. In my form, I'm using htmlarea boxes to edit and style text fields. The problem I have is that when I'm clicking on "save changes", the browser reload the form page making some cleaning (removing a lot of tags, including allowed ones), before passing the datas to the "action" file. I'm working on this since three days without being able to understand what is done by the submit button.
Any idea?

Thanks
Franck