Hi Chris - You are right on this for both accounts... I don't believe that the POST SQL is for Facebook and Twitter Login, only using the standard login... I will have to check but this is my initial thoughts, we will need to get this added for the next release.
If this was working though
The trouble here is that I think you are correct about the cache issues. So... Hmmm... Not sure what could be done here, I know for initial registration you can use the "Silent Post" to Dynamic Registration which should be able to handle an "Add Security Role" completion event?
Check out this thread and let me know if this helps:
http://www.datasprings.com/dnn-modules/dynamic-login/silent-post-to-dynamic-registration-for-facebook-integration
Thanks,
Chad