Do you have E-Mail cloaking turned on?
Yes, I do.
One option is to ditch the contact form and use a form extension that comes with captcha support.
I now dropped com_contact and uploaded dfcontact with com_securityimages (SI) support. Due to changes in SI 5.x dfcontact does not work any more properly with SI.
I managed to change (with the help of others
)the source of dfcontact to get SI running again. So I've solved this task yesterday ;D