Hi,
On the SimpleSimon template page it says:
SD Simple Simon template is intended ONLY for content display. Do not use SD Simple Simon to render forms, you WILL get errors and your form will not render. Use the default seb_onetemplate (or other) for forms.
But for a search form - it works? (I'm using it for one and I see no errors... so... am I a magician or is it supposed to work?) :)