Are you sure you selected the correct field to synchronize as the default form integration included with CB already provides these fields and you may have selected them by mistake perhaps.
Enable debug mode and maximum error reporting in Joomla global configuration. Once done attempt to save your profile and see if any error occurs. Please note CB Forums must be enabled within CB > Plugin Management for this to take affect. Also ensure CB Forums is up to date (latest is 2.1.4).
Any documentation?
Nope, professional plugins don't come with documentation.
If issue persists please PM backend super administrator login credentials and will need to debug the plugin as it's possible it could be a bug; I do not have K1.7 anymore and all my dev environments are now K2.0.