The problem can be seen with the following code:

    public partial class Form1 : Form
    {
        TChart _tChart1;
        SplitContainer _splitContainer;
        Button _button;
        public Form1()
        {
            InitializeComponent();

            _splitContainer = new SplitContainer();
            _splitContainer.Dock = DockStyle.Fill;
            Controls.Add(_splitContainer);

            _tChart1 = new TChart();
            _tChart1.Dock = DockStyle.Fill;
            _tChart1.Series.Add(typeof(Bar)).FillSampleValues();
            _splitContainer.Panel2.Controls.Add(_tChart1);

            _button = new Button();
            _button.Text = "Click";
            _button.Click += _button_Click;
            _splitContainer.Panel1.Controls.Add(_button);

        }

        private void _button_Click(object sender, System.EventArgs e)
        {
            _tChart1.CurrentTheme = ThemeType.BlackIsBack;
        }
    }