Defaulting Inventory Dispositions to Blank or Null

I have done some cursory tests and cannot get the system to default to blank when Parts are added to Affected Data.  I cleared the default value and I do have an Enumerated list of values for each Inventory Disposition column.  I want to ensure there is positive indicators of a choice for Inventory Dispositions, not just accepting the defaults. Ideally, I would like blank to show up indicating that nothing was selected yet. Tried restarting server but seems to always default to first value in enumerated list though blank is a choice on the row above in drop down.  I do not have a setting that value is required in constraints.