Adding a Column to the Supplier Price List Part Search

I followed the code example in this topic

private void oTrans_adapter_BeforeAdapterMethod(object sender, BeforeAdapterMethodArgs args)
	{
		// ** Argument Properties and Uses **
		// ** args.MethodName **
		// ** Add Event Handler Code **

		// ** Use MessageBox to find adapter method name
		// EpiMessageBox.Show(args.MethodName)
		switch (args.MethodName)
		{
			case "GetList":
			case "GetRows":
				EpiSearchBase adapterSearchForm = oTrans_adapter.SearchForm;

				if (adapterSearchForm != null)
            	{
    	            adapterSearchForm.ClearEpiSearchColumns();
 
        	        // Parameters: Data Column Name, Column Header Text, Width, Is Result, Position
            	    adapterSearchForm.SetEpiSearchColumn(new EpiSearchColumn("PartNum", "Part Num", -1, true, 0), true);
					adapterSearchForm.SetEpiSearchColumn(new EpiSearchColumn("PartDescription", "Description", -1, true, 1), true);
    	            adapterSearchForm.SetEpiSearchColumn(new EpiSearchColumn("EffectiveDate", "Effective Date", -1, true, 2), true);
         	       adapterSearchForm.SetEpiSearchColumn(new EpiSearchColumn("PUM", "UOM", -1, true, 3), true);
            	}
				break;
		}
	}

This code does work, however, I cannot explain why there is an additional column called Operation that concatenated into the 5th column… Any ideas?