Just in case it saves someone else the several hours of insanity I just
went through, update_attributes will not save unless the model
validations are satisfied, but update_attribute (the singular form)
will save the attribute to the database even if the model validations
This appears to be a feature, not a bug
(http://api.rubyonrails.com/classes/ActiveRecord/Base.html) although it
is not mentioned in Agile Web Dev with Rails (page 221).