Collapsing and Expanding SplitContainer panels

I have 3 split containers in my winform application. splitContainer1, splitContainer2, splitContainer3

splitContainer1 is the main split container. in it's panel1 I put splitContainer2 and in its panel2 I have splitContainer3

I then added two buttons to collapse/hide splitContainer3 panels: whenever I click on a button, it gets collapsed, but when I want 2 panels be collapsed, one of them automatically gets expanded again What can be the problem?

private void btToggleCI_Click(object sender, EventArgs e){    switch (splitContainer3.Panel1Collapsed)    {        case false:            splitContainer3.Panel1Collapsed = true;            btToggleCI.ForeColor = Color.Gray;            break;        case true:            splitContainer3.Panel1Collapsed = false;            btToggleCI.ForeColor = Color.Black;            break;    }}private void btToggleTestPlan_Click(object sender, EventArgs e){    switch (splitContainer3.Panel2Collapsed)    {        case false:            splitContainer3.Panel2Collapsed = true;            btToggleTestPlan.ForeColor = Color.Gray;            break;        case true:            splitContainer3.Panel2Collapsed = false;            btToggleTestPlan.ForeColor = Color.Black;            break;    }}