What's the strangest corner case you've seen in C# or .NET?

This one had me truly puzzled (I apologise for the length but it's WinForm). I posted it in the newsgroups a while back.

I've come across an interesting bug. I
have workarounds but i'd like to know
the root of the problem. I've stripped
it down into a short file and hope
someone might have an idea about
what's going on.

It's a simple program that loads a
control onto a form and binds "Foo"
against a combobox ("SelectedItem")
for it's "Bar" property and a
datetimepicker ("Value") for it's
"DateTime" property. The
DateTimePicker.Visible value is set to
false. Once it's loaded up, select the
combobox and then attempt to deselect
it by selecting the checkbox. This is
rendered impossible by the combobox
retaining the focus, you cannot even
close the form, such is it's grasp on
the focus.

I have found three ways of fixing this
problem.

a) Remove the binding to Bar (a bit
obvious)

b) Remove the binding to
DateTime

c) Make the DateTimePicker
visible !?!

I'm currently running Win2k. And .NET
2.00, I think 1.1 has the same problem. Code is below.

using System;
using System.Collections;
using System.Windows.Forms;
namespace WindowsApplication6
{
    public class Bar
    {
        public Bar()
        {
        }
    }
    public class Foo
    {
        private Bar m_Bar = new Bar();
        private DateTime m_DateTime = DateTime.Now;
        public Foo()
        {
        }
        public Bar Bar
        {
            get
            {
                return m_Bar;
            }
            set
            {
                m_Bar = value;
            }
        }
        public DateTime DateTime
        {
            get
            {
                return m_DateTime;
            }
            set
            {
                m_DateTime = value;
            }
        }
    }
    public class TestBugControl : UserControl
    {
        public TestBugControl()
        {
            InitializeComponent();
        }
        public void InitializeData(IList types)
        {
            this.cBoxType.DataSource = types;
        }
        public void BindFoo(Foo foo)
        {
            this.cBoxType.DataBindings.Add("SelectedItem", foo, "Bar");
            this.dtStart.DataBindings.Add("Value", foo, "DateTime");
        }
        /// 

        /// Required designer variable.
        /// 
        private System.ComponentModel.IContainer components = null;
        /// 

        /// Clean up any resources being used.
        /// 
        /// true if managed resources should be disposed; otherwise, false.
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }
        #region Component Designer generated code
        /// 

        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// 
        private void InitializeComponent()
        {
            this.checkBox1 = new System.Windows.Forms.CheckBox();
            this.cBoxType = new System.Windows.Forms.ComboBox();
            this.dtStart = new System.Windows.Forms.DateTimePicker();
            this.SuspendLayout();
            //
            // checkBox1
            //
            this.checkBox1.AutoSize = true;
            this.checkBox1.Location = new System.Drawing.Point(14, 5);
            this.checkBox1.Name = "checkBox1";
            this.checkBox1.Size = new System.Drawing.Size(97, 20);
            this.checkBox1.TabIndex = 0;
            this.checkBox1.Text = "checkBox1";
            this.checkBox1.UseVisualStyleBackColor = true;
            //
            // cBoxType
            //
            this.cBoxType.FormattingEnabled = true;
            this.cBoxType.Location = new System.Drawing.Point(117, 3);
            this.cBoxType.Name = "cBoxType";
            this.cBoxType.Size = new System.Drawing.Size(165, 24);
            this.cBoxType.TabIndex = 1;
            //
            // dtStart
            //
            this.dtStart.Location = new System.Drawing.Point(117, 40);
            this.dtStart.Name = "dtStart";
            this.dtStart.Size = new System.Drawing.Size(165, 23);
            this.dtStart.TabIndex = 2;
            this.dtStart.Visible = false;
            //
            // TestBugControl
            //
            this.AutoScaleDimensions = new System.Drawing.SizeF(8F, 16F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.Controls.Add(this.dtStart);
            this.Controls.Add(this.cBoxType);
            this.Controls.Add(this.checkBox1);
            this.Font = new System.Drawing.Font("Verdana", 9.75F,
            System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point,
            ((byte)(0)));
            this.Margin = new System.Windows.Forms.Padding(4);
            this.Name = "TestBugControl";
            this.Size = new System.Drawing.Size(285, 66);
            this.ResumeLayout(false);
            this.PerformLayout();
        }
        #endregion
        private System.Windows.Forms.CheckBox checkBox1;
        private System.Windows.Forms.ComboBox cBoxType;
        private System.Windows.Forms.DateTimePicker dtStart;
    }
    public class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            this.Load += new EventHandler(Form1_Load);
        }
        void Form1_Load(object sender, EventArgs e)
        {
            InitializeControl();
        }
        public void InitializeControl()
        {
            TestBugControl control = new TestBugControl();
            IList list = new ArrayList();
            for (int i = 0; i < 10; i++)
            {
                list.Add(new Bar());
            }
            control.InitializeData(list);
            control.BindFoo(new Foo());
            this.Controls.Add(control);
        }
        /// 

        /// Required designer variable.
        /// 
        private System.ComponentModel.IContainer components = null;
        /// 

        /// Clean up any resources being used.
        /// 
        /// true if managed resources should be disposed; otherwise, false.
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }
        #region Windows Form Designer generated code
        /// 

        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// 
        private void InitializeComponent()
        {
            this.components = new System.ComponentModel.Container();
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.Text = "Form1";
        }
        #endregion
    }
    static class Program
    {
        /// 

        /// The main entry point for the application.
        /// 
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
    }
}