I wasted a chunk of time running in circles over this issue.  I had assumed that when I loaded the fixtures into my database via ‘rake db:fixtrues:load’ or ‘rake spec:db:fixtures:load’ in Ruby on Rails that it was blowing away all the data in all of my tables before creating records. It turns out that it only blows away data in tables for which you have fixtures, leaving any generated cruft in other tables behind.