[SOLVED] Why does CB create duplicates in the db?

I have massive difficulties with the registrstion anyway and now even with no conditional field at all I get even this:

1062 - Duplicate entry '435' for key 'PRIMARY' SQL=INSERT INTO `xz685_comprofiler` (`id`,`user_id`,`firstname`,`lastname`,`approved`,`confirmed`,`registeripaddr`,`cb_businessname`,`cb_country`,`cb_zipcode`,`cb_city`,`cb_street`,`cb_additionaldetails`,`cb_phone`,`cb_mobilephone`,`cb_skype`,`cb_website`,`cb_facebook`,`cb_vat`) VALUES ('435','435','first','name','1','0','::1','coti','country_Spain_195','35660','El Cotillo','Calle Requena, 9','','','','','','','')

Why does CB not take care of duplicates? No I have to code an AJAX call to check for the next available id and have to set that in the form? What is the benefit of that?

Have you recently run all the CB database tools in the backend?

That helped indeed. Thanks. Do I have to do this every time a user registers?

Ideally: no
If your Joomla+CB are set up correctly you won't need to run them again. However, if you or another plugin change the user tables these tools need to be run.
In my case sometimes other admins forget to use the CB user manager instead of the Joomla one. I run the tools every couple of weeks during normal use.
If you encounter this error message again you should try to pinpoint who or what causes it.