To reproduce: 
1.Add a RadGridView with several levels of hierarchy. 
2.Apply Office2007Silver theme.

When clicking over the "+" sign, it seems to be a refresh problem for the GridIndentCellElement. Please, refer to the attached picture.

Workaround:
private void radGridView1_ViewCellFormatting(object sender, Telerik.WinControls.UI.CellFormattingEventArgs e)
{
    if (e.CellElement is GridIndentCellElement)
    {
        e.CellElement.BackColor = Color.FromArgb(231, 231, 231);
        e.CellElement.DrawFill = true;
        e.CellElement.GradientStyle = GradientStyles.Solid;
    }
    else
    {
        e.CellElement.ResetValue(LightVisualElement.BackColorProperty, ValueResetFlags.Local);
        e.CellElement.ResetValue(LightVisualElement.DrawFillProperty, ValueResetFlags.Local);
        e.CellElement.ResetValue(LightVisualElement.GradientStyleProperty, ValueResetFlags.Local);
    }
}