AFAIU: This module is not needed

hook_form_alter is simply misundestood. It does not mean "alter when the form gets shown". It means "alter when its build. And a preview with validation errors or a save with validation errors does not mean rebuild ( if it is a cached for though ).

To properly do this, use after_build which is called everytime the form gets shown (eventhough it is again called "build"... )

http://github.com/EugenMayer/wysiwyg_imageupload/blob/master/wysiwyg_ima...

And finally the implementation

http://github.com/EugenMayer/wysiwyg_imageupload/blob/master/wysiwyg_ima...

I guess the FAPI is far to complex and in that manner the workflow / flow of forms is pretty much undcoumented and has very odd edge cases.