Use the attached project to reproduce.

Workaround:
private void RadForm1_SizeChanged(object sender, EventArgs e)
{
    if (this.WindowState == FormWindowState.Normal)
    {
        this.SizeChanged -= RadForm1_SizeChanged;
        this.Size = new Size(this.Size.Width + 1, this.Size.Height + 1);
        this.Size = new Size(this.Size.Width - 1, this.Size.Height - 1);

        this.SizeChanged += RadForm1_SizeChanged;
    }
}