To reproduce:
public Form1()
{
    InitializeComponent();
  
    RadButton bt = new RadButton();
    bt.Dock = DockStyle.Right;
    bt.Parent = this;

    RadTitleBar tb = new RadTitleBar();
    tb.Dock = DockStyle.Top;
    tb.Parent = this;
    tb.Size = new Size(150, 100);

    this.Shape = new RoundRectShape(20);
    this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.Sizable;    
}