To reproduce:
- Subscribe to the CellClick event 
- Click several times in the grid with the right mouse button. 
- At some point, the CellClick event will be executed. 

Workaround:
- Use the Click event:

private void RadGridView1_Click(object sender, EventArgs e)
{
    var args = e as MouseEventArgs;
    if (args.Button == MouseButtons.Left)
    {
        var clickedCell = radGridView1.ElementTree.GetElementAtPoint(args.Location) as GridDataCellElement;
        if (clickedCell != null)
        {
            //add your code here
        }
    }
}