Process function is not called when submitting, redirects to home page

[selay]

All was good until recently.
Our customer reported that when they submit a form, it goes to home page and there is no submission recorded in the admin.
While investigating, I found out that the post data are submitted to Form function and it is there, but it never reaches "process" function?
How is process function supposed to be called?

[selay]

Actually, I found out what happened.
Seems on validation error, it redirects back to the form if referrer is set. Otherwise, it goes to homepage, losing form data.
Our sites use referrer =never in html meta tag, which breaks the form.