To reproduce:

Add a RadGridView and three GridViewComboBoxColumns with repetitive values:

for (int i = 0; i < 3; i++)
{
    List<int> datasource = new List<int>();
    for (int j = 0; j < 12; j++)
    {
        datasource.Add(j);
    }
    this.Grid.Columns.Add(new GridViewComboBoxColumn()
        {
            DataSource = datasource
        });
}

for (int i = 0; i < 10; i++)
{
    for (int j = 0; j < 5; j++)
    {
        this.Grid.Rows.Add(i, i, i);
    }
}

Start the project and sort second and last column by the same value and make sure that you have vertical scrollbar.

Select a cell in the second column change its value and press the tab key(or click on another cell in the same row). You will see that the scrollbar will go to the bottom of the grid.

Workaround:

Use the following class:

public class ActionExecuteHelper
    {
        #region Singleton

        private static ActionExecuteHelper instance;
        private static readonly object syncRoot = new object();

        public static ActionExecuteHelper Instance
        {
            get
            {
                if (instance == null)
                {
                    lock (syncRoot)
                    {
                        if (instance == null)
                        {
                            instance = new ActionExecuteHelper();
                        }
                    }
                }
                return instance;
            }
        }

        #endregion

        private readonly Timer timer;

        public ActionExecuteHelper()
        {
            this.timer = new Timer();
        }

        public void ExecuteDelayedAction(Action action, int delayInMilliseconds)
        {
            EventHandler timerTick = null;

            timerTick = delegate
            {
                this.timer.Stop();
                this.timer.Tick -= timerTick;
                action.Invoke();
            };

            this.timer.Tick += timerTick;
            this.timer.Interval = delayInMilliseconds;
            this.timer.Start();
        }
    }


And use it with the following code

private int savedValue;
private void Grid_CellEndEdit(object sender, GridViewCellEventArgs e)
{
    this.Grid.TableElement.VScrollBar.ValueChanged += ValueChangedDelegate;
}

private void ValueChangedDelegate(object sender, EventArgs e)
{
    this.Grid.TableElement.VScrollBar.ValueChanged -= ValueChangedDelegate;
    ActionExecuteHelper.Instance.ExecuteDelayedAction(new Action(this.SetScrollbarValue), 5);
}

private void SetScrollbarValue()
{
    this.Grid.TableElement.VScrollBar.Value = savedValue;
}

private void Grid_ValueChanging(object sender, ValueChangingEventArgs e)
{
    this.savedValue = this.Grid.TableElement.VScrollBar.Value;
}

This way the value of the scrollbar will be saved and restored.