Multiple User Profiles using multi-table inheritance and Userena

[James Rivett-Carnac]

This is a question that gets asked in many forms, but I am having issues with the multi-table inherence method of doing this with Userena.  I have strong reasons for needing multiple profile types which I won't go into here. i put example code in the following gist:
https://gist.github.com/2792846#comments

In short, I have a common profile (CommonProfile which two profiles (SpamProfile and EggsProfile) inherit from.  I override the signup form to save data into the derived SpamProfile, but no data is stored in the derived profile table, so all the users end up with CommonProfiles only, which should not be aloud.

I'm at a bit of a loss as to what to do next to fix this.