Radar, 
I added a test to demonstrate the problem.  See products_controller_spec.rb "can update a product when count_on_hand is given".   When you pass params[:product] instead of product_params in @product.update_attributes it will fail.  option_types, variants, product_properties and count_on_hand cannot be passed, I tried it out.  (manual, no tests :-()  permalink and taxon_ids don't seem to cause a problem.  I changed it, that's why I closed the previous pull-request and created a new one.