Font causes GDI leak in custom control

I have created a custom control like below.

public partial class TextBoxEx : TextBox
{
    public TextBoxEx()
    {
        InitializeComponent();
        Font = Utility.normalFont;
    }

    protected override void OnPaint(PaintEventArgs pe)
    {
        base.OnPaint(pe);
    }
}
    //A utility class to initialize font.   
    class Utility
    {
        
        internal static Font normalFont = new Font("Arial", 18);
    }

I have two forms Form1 and Form2. This TextBoxEx is added to Form2. I am showing Form2 when clicking a button in Form1.

Continuously showing and closing Form2 causes GDI leak in my application. After analysing with a GDI detection tool(Bear.exe), it is found that the Font causes GDI leak.

My question is,
1. Why the Font is not released even though Dispose() method of TextBoxEx is get called.(While closing Form2, Dispose() method of TextBoxEx will be invoked automatically).
2. How can I solve GDI leak caused by Font?.
(Font.Dispose() cannot be called in Dispose() method of TextBoxEx. Because it throws "Parameter is not valid" exception in the constructor).

Tags: C#, .NET, GDI, Windows Forms, Custom controls