I've got a problem with Captcha validation, using it with a form created by my own module.
Using Captcha with e.g. a Webform in the same installation works fine.
I've added the Captcha via the configuration page to the form created by my custom module. Captcha is showing up and looks fine, even the output for captcha in $form_state is the same as with the other form in which it is working fine.
But whatever I enter, or even if I don't enter anything and the Captcha input field is left empty, there's no Captcha validation, it let's me pass through to the next page while it should keep me on the page with the form. No error message shown.
Does anybody know a possible reason for that? I've read about some issues with Ajax but I'm not using any other Ajax stuff in that form or on that page. The error appears with different Captcha types, Image as well as Math. Also with different browsers, computers, users logged in and not logged in.