Hi,

This time I had to remove the stored form data from the browser at the end to be able to register a new user.

I believe, the name of the form element , i.e. the text field name phone, is the problem. It seems to be a real honeypot on your local system.

autocomplete="off" in my HTML5-using-theme because it's my only idea to solve this. I hope that it works.

I don't think so. Maybe, it works for some browsers but it is not a comprehensive solution.

/Micha