I found the offending 3rd party module. I bought in on Snowcovered a year ago. It's still for sale:
http://www.snowcovered.com/Snowcovered2/Default.aspx?tabid=242&PackageID=3854
It was provided by Darren Neese of DNNRocks:
http://www.dotnetnukerocks.com/
http://www.neeseconsulting.com/tabid/1350/Default.aspx
It was marketed as a user defined table, but it overwrote the core UDT tables, contained glaring bugs and didn't come with any uninstall scripts.
When I suggested he should not meddle with the core modules and provide uninstall functionality with any modules he sold on Snowcovered he became angry that I used the word "should" and refused further correspondence.
Here is a snippet from our last email dialog.
Wylie: I think these kinds of errors would be caught before release if you had a more rigorous user testing policy.
Neese: I appreciate your feedback on the module itself. However, for the last time I will state, I have no interest in what you think what should or should not be caught when, or how I release whatever I choose.
Hope this helps anyone else who had the misfortune of dealing with this guy.
Wylie