To reproduce:
- Put  grid and collapsible panel to a form.
- Set the Dock of the grid to fill.
- Set the Dock of the panel to top.
- Expand the panel, you will notice that the panel is drawn over the grid.

Workaround:
 
public RadForm1()
{
    InitializeComponent();
    radGridView1.Anchor = AnchorStyles.None;
    radCollapsiblePanel1.Dock = DockStyle.Top;
    radCollapsiblePanel1.EnableAnimation = false;

    radCollapsiblePanel1.Expanded += radCollapsiblePanel1_Expanded;
    radCollapsiblePanel1.Collapsed += radCollapsiblePanel1_Collapsed;

    gridSmallsize = new Size(this.Width - 10, this.Height - 190);
    gridLargeSize = new Size(this.Width - 10, this.Height - 60);
}

Size gridSmallsize;
Size gridLargeSize;

void radCollapsiblePanel1_Collapsed(object sender, EventArgs e)
{
    radGridView1.Size = gridLargeSize;
    radGridView1.Location = new Point(0, 30);
}

void radCollapsiblePanel1_Expanded(object sender, EventArgs e)
{
    radGridView1.Size = gridSmallsize;
    radGridView1.Location = new Point(0, 160);
}