SetOnUndone & SetOnRedone - What am I doing wrong?

Main.cs

private void AddSelectedToTemp()
{
    QueuedTask.Run(() =>
    {
        using (FeatureClass tempSegsFC = TempSegmentsLayer.GetFeatureClass())
        using (RowCursor segmentsCursor = SegmentsLayer.GetSelection().Search((QueryFilter)null, false))
        {
            EditOperation operation = new EditOperation();
            operation.Name = "add selected to temp segments";
            bool newPartCreated = false;
            operation.Callback(context =>
            {
                while (segmentsCursor.MoveNext())
                {
                    string id = GetUSNGID_Line(segmentsCursor.Current);
                    RowBuffer tempRowBuf = CopyRowValues(segmentsCursor.Current, tempSegsFC);
                    tempRowBuf["USNG_SEG"] = id;
                    if (tempSegmentIDs.Contains(id))
                    {
                        currentPart++;
                        tempSegmentIDs.Clear();
                        newPartCreated = true;
                    }
                    tempSegmentIDs.Add(id);
                    tempRowBuf["RoutePart"] = currentPart;
                    tempSegsFC.CreateRow(tempRowBuf);
                    tempRowBuf.Dispose();
                }
                context.Invalidate(tempSegsFC);
            }, tempSegsFC);
            if (newPartCreated)
            {
                // NOT WORKING ref: https://community.esri.com/message/733381-re-examples-for-setonundone-setonredone-setoncomitted?commentID=733381#comment-733381
                operation.SetOnUndone(() =>
                {
                    currentPart--;
                });
                operation.SetOnRedone(() =>
                {
                    currentPart++;
                });
            }

            bool success = operation.Execute();
            if (success)
            {
                SegmentsLayer.ClearSelection();
            }
        }
    });
}