Catalog reference variable Drop down value is showing unwanted values

Hi Experts, 

I'm trying to configure a catalog variable which uses a reference qualifier to show multiple columns in drop down list, 

i'm using the below mentioned attributes, 

ref_auto_completer=AJAXTableCompleter, 
ref_ac_columns =asset;task;location,
ref_ac_columns_search=true,
ref_ac_display_value=true

but it's showing an additional column "sys_created_on" 

display value on referenced table for "sys_created_on" field is false. 

Kindly guide me to navigate through this requirement. 

Regards, 

Varun Sharma