Adding a captcha, either through captcha admin or using hook_form_alter, to a views exposed filter form
1) loads initially with
* Math question field is required.
* The answer you entered for the CAPTCHA was not correct.
2) after submission incorrectly gives:
The answer you entered for the CAPTCHA was not correct.
reproduced by another user here:
"It seems an exposed view filter form is automatically submitted (before you get the chance to fill it in) in order to show a default view."