i should also note that i was also using a custom created race, and all of the relationships were created normally without problems (both prior and after the 1.6 update)
since i don't believe i have a magic version of the CK, i think there might be something that you and the others who reported the same problem might be overlooking. sorry if this isnt of any help, but i am strongly against reporting bugs that arent actually bugs (if you can outline a set of conditions in which this is repeatable for anyone, i would be convinced it is a bug, but since i was able to successfully create the relationships using the conditions you listed, i dont think there is a bug)
suppose you did manage to get bethesda to look at this, and they cant recreate the bug on their end either? how exactly are they supposed to fix it?
The thing is that several people are posting on these tutorial videos about the same exact error and I am sure that not all of them are doing the same thing I am doing with a custom race. Here's a way for you to test whether its an error or not. You uninstall your creation kit right now then redownload and install it. Course if yours isnt broken that would be dumb now wouldnt it cause you'd probably get the broken version. Just cause your version number is the same as everyone else doesn't necessarily mean that there is not a version, labeled exactly the same that doesn't have exactly the same coding which is what is currently downloadable.
I'm going to unistall my creation kit again and redownload it again for the third time today and try to create a character without the custom race...again today....and maybe this time I'll get lucky. I've gone through this process a few times over and have still been getting this same error. I also have attempted to create a standard follower not of a custom race from just the Skyrim esp data and the issue is continuous. Since my version of Skyrim was reinstalled not but three days ago this has to be an error. I have created custom followers dozens of times in the past and this error has never been an occurance until 1.6.
I am positive this is a bug and wouldn't bring it up to Bethesda if I was not certain.