Recently I discovered all the product positions after being assigned to a category were defaulted to 1. I needed to change this number to anything other than 1.
I found that Magento currently defaults this number to 1 in their resource model under the function _saveCategories. The entire class would be Mage_Catalog_Model_Resource_Product.
In order to solve this problem I decided to do a quick rewrite of this resource model. You should rewrite this class in your modules config file like so.
Then create the file Module_Name_Model_Catalog_Resource_Product and extend Mage_Catalog_Model_Resource_Product