public class BaseRadForm : RadForm
{
    private Size cachedSize;
    private Size sizeNormal;

    protected override void OnShown(EventArgs e)
    {
        base.OnShown(e);

        this.sizeNormal = this.ClientSize;
    }

    protected override void OnActivated(System.EventArgs e)
    {
        if (this.WindowState == FormWindowState.Minimized)
        {
            this.WindowState = FormWindowState.Normal;
            this.ClientSize = sizeNormal;
        }
        else if (this.cachedSize != Size.Empty && this.Size != this.cachedSize)
        {
            this.Size = this.cachedSize;
        }

        base.OnActivated(e);
    }

    protected override void OnDeactivate(System.EventArgs e)
    {
        this.cachedSize = this.Size;
        base.OnDeactivate(e);
    }
}