Filtering Acumatica Grid with Custom Column Values

I added a new column to the grid in the "Prepare Replenishment" screen (IN50800) please refer the image below: 

Please note that I have marked the column header which is added as a custom column.

Please refer the code below:

namespace PX.Objects.IN.S
{
    public class INItemSiteExt : PXCacheExtension<INItemSite>
    {
        public class ProgNameAttributeID : BqlString.Constant<ProgNameAttributeID>
        {
            public ProgNameAttributeID() : base("PROGNAME") { }
        }

        #region UsrProgramName

         PXString(255, IsUnicode = true)]
         PXUIField(DisplayName = "Program Name")]
        public virtual string UsrProgramName { get; set; }
        public abstract class usrProgramName : BqlString.Field<usrProgramName> { }

        #endregion
    }
}

Graph extension:

namespace PX.Objects.IN
{
    public class INReplenishmentCreate_Extension : PXGraphExtension<INReplenishmentCreate>
    {


        #region Event Handlers

        protected void INReplenishmentItem_RowSelected(PXCache cache, PXRowSelectedEventArgs e)
        {
            INReplenishmentItem row = e.Row as INReplenishmentItem;
            if (row == null) return;

            var item = (InventoryItem)PXSelectorAttribute.Select<INReplenishmentItem.inventoryID>(cache, row);
            if (item != null)
            {
                var attribute = (CSAnswers)PXSelect<CSAnswers,
                                Where<CSAnswers.refNoteID, Equal<Required<InventoryItem.noteID>>,
                                And<CSAnswers.attributeID, Equal<Required<CSAnswers.attributeID>>>>>
                                .Select(Base, item.NoteID, "PROGNAME");

                if (attribute != null)
                {
                    cache.SetValueExt<INItemSiteExt.usrProgramName>(row, attribute.Value.Trim());
                }
            }
        }

        #endregion

    }
}

With above code it populates the values to the new added column but if I want to filter by it. Like below:

It doesn't filter most of the values, but sometimes it searches the first row of the grid. Otherwise it shows nothing.

Can anyone find any issues here or missing thing?