How to reproduce: 
partial class Form2
    {
        /// <summary>
        /// Required designer variable.
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows Form Designer generated code

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            this.radTrackBar1 = new Telerik.WinControls.UI.RadTrackBar();
            ((System.ComponentModel.ISupportInitialize)(this.radTrackBar1)).BeginInit();
            this.SuspendLayout();
            // 
            // radTrackBar1
            // 
            this.radTrackBar1.Anchor = ((System.Windows.Forms.AnchorStyles)((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Right)));
            this.radTrackBar1.BackColor = System.Drawing.Color.FromArgb(((int)(((byte)(233)))), ((int)(((byte)(240)))), ((int)(((byte)(249)))));
            this.radTrackBar1.Font = new System.Drawing.Font("Segoe UI", 8.25F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(0)));
            this.radTrackBar1.LabelStyle = Telerik.WinControls.UI.TrackBarLabelStyle.BottomRight;
            this.radTrackBar1.LargeChange = 5;
            this.radTrackBar1.LargeTickFrequency = 139;
            this.radTrackBar1.Location = new System.Drawing.Point(36, 69);
            this.radTrackBar1.Maximum = 140F;
            this.radTrackBar1.Minimum = 1F;
            this.radTrackBar1.Name = "rTrackBar1";
            this.radTrackBar1.Size = new System.Drawing.Size(243, 33);
            this.radTrackBar1.SmallTickFrequency = 5;
            this.radTrackBar1.SnapMode = Telerik.WinControls.UI.TrackBarSnapModes.None;
            this.radTrackBar1.TabIndex = 0;
            this.radTrackBar1.Text = "rTrackBar1";
            this.radTrackBar1.ThemeName = "ControlDefault";
            this.radTrackBar1.TickStyle = Telerik.WinControls.Enumerations.TickStyles.None;
            this.radTrackBar1.Value = 80F;
            ((Telerik.WinControls.UI.RadTrackBarElement)(this.radTrackBar1.GetChildAt(0))).MinSize = new System.Drawing.Size(100, 0);
            ((Telerik.WinControls.UI.TrackBarBodyElement)(this.radTrackBar1.GetChildAt(0).GetChildAt(1))).Margin = new System.Windows.Forms.Padding(7, 0, 7, 0);
            ((Telerik.WinControls.UI.TrackBarScaleContainerElement)(this.radTrackBar1.GetChildAt(0).GetChildAt(1).GetChildAt(0))).Orientation = System.Windows.Forms.Orientation.Vertical;
            ((Telerik.WinControls.UI.TrackBarScaleElement)(this.radTrackBar1.GetChildAt(0).GetChildAt(1).GetChildAt(0).GetChildAt(2))).Orientation = System.Windows.Forms.Orientation.Vertical;
            ((Telerik.WinControls.UI.TrackBarScaleElement)(this.radTrackBar1.GetChildAt(0).GetChildAt(1).GetChildAt(0).GetChildAt(2))).StretchVertically = false;
            ((Telerik.WinControls.UI.TrackBarLabelContainerElement)(this.radTrackBar1.GetChildAt(0).GetChildAt(1).GetChildAt(0).GetChildAt(2).GetChildAt(1))).StretchVertically = false;
            ((Telerik.WinControls.UI.TrackBarLabelElement)(this.radTrackBar1.GetChildAt(0).GetChildAt(1).GetChildAt(0).GetChildAt(2).GetChildAt(1).GetChildAt(0))).Text = "Lo";
            ((Telerik.WinControls.UI.TrackBarLabelElement)(this.radTrackBar1.GetChildAt(0).GetChildAt(1).GetChildAt(0).GetChildAt(2).GetChildAt(1).GetChildAt(1))).Text = "Hi";
            // 
            // Form2
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(822, 515);
            this.Controls.Add(this.radTrackBar1);
            this.Name = "Form2";
            this.Text = "Form2";
            ((System.ComponentModel.ISupportInitialize)(this.radTrackBar1)).EndInit();
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        #endregion

        private Telerik.WinControls.UI.RadTrackBar radTrackBar1;
    }

Workaround: remove setting of the text from the designer file to the Shown event of the form
public partial class Form2 : Form
{
    public Form2()
    {
        InitializeComponent();
    }

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

        ((Telerik.WinControls.UI.TrackBarLabelElement)(this.radTrackBar1.GetChildAt(0).GetChildAt(1).GetChildAt(0).GetChildAt(2).GetChildAt(1).GetChildAt(0))).Text = "Lo";
        ((Telerik.WinControls.UI.TrackBarLabelElement)(this.radTrackBar1.GetChildAt(0).GetChildAt(1).GetChildAt(0).GetChildAt(2).GetChildAt(1).GetChildAt(1))).Text = "Hi";
    }
}

 How to reproduce
1. Drag a RadTrackBar from the toolbox
2. Set the Maximum property, e.g. to 100, set the Minimum property, e.g. to 50
3. Close and reopen the designer, you will notice that the Minimum property of the control is not the expected value of 50, although it has been properly serialized in the designer file.

Workaround: 
set the Minimum property in the Load event of the form