JDE Enterprise One 9.0 Sales order processing with preference user price codes

I am using preferences for user price codes.      When i enter an order with P4210,  the UPC1 is being populated based on my preference.  

When I maintain the order,  should i be able to override the UPC1 and replace it with the valid blank udc value?   

My P4210 will allow me to change the UPC1 with another valid non-blank udc value but it will not allow me to enter a blank value.

When I enter a blank value on a change order  it re-retrieves the original UPC1 from the preference.  

My question is -  Is this standard JDE    Is there some setting somewhere that is preventing me from override or is it just generally not allowed?