UPDATE: The latest rails has fixed this problem but this problem was still present in Rails 2.2.2.
The new dirty methods in Rails show this interesting result:
The above code has position as a nullable integer column. When parameters come in a post via the parameters hash position comes across as a string. For 14 you get the Rails goodness and assigning "14" is not seen as a change - but why not the same thing for 0?
The problem is in the following offending code in vendor/rails/activerecord/lib/active_record/dirty.rb file. I have commented out the problem line (look for the no!!!!...) and added what I believe to be the correct code below it: