Integration of sr_freecap is useless as server side validation is broken

For a customer project I try to set up femanager with sr_freecap. 

During my tests I discovered, that the server side validation is working fine as long I provide any string in the captcha field. If I leave it alone and empty the captcha field is not validated at all - not even the CaptchaValidator is called. 

Adding min or required to the configuration doesn't change anything. 