Strange behavior using WinForms autoscroll

Question

I am working on a projet with Microsoft VisualStudio Forms .NET 4.0 c#. I want to scroll on my forms page entirely, not on a precise object. I created a panel object called main_panel, which is the only child object of this (my forms page). It has a height of 1.6 times the client_size. I activated this.autoscroll = true. The problem is that when I shrank my window horizontally, the scroll bar allows me to scroll beyond my main_panel. When I resize in any other way, it works completly fine.

I checked :

• main_panel is the ONLY child object of this.
• the scroll is indeed beyond the main_panel's height, which is correctly defined.
• margins of main_panel and this are set to 0.
• this bug is happening on multiple computers

Here is a code I have written that reproduces this bug :

namespace My_forms
{
    public partial class Test : Form
    {
        public Test()
        {
            InitializeComponent();

        }

        private void Test_Load(object sender, EventArgs e)
        {
            main_panel.BackColor = Color.Red;
            main_panel.Location = new Point(0, 0);

            this.Controls.Add(main_panel);
            this.AutoScroll = true;
        }

        private void Test_SizeChanged(object sender, EventArgs e)
        {
            main_panel.Size = new Size((int)ClientSize.Width, (int)(ClientSize.Height * 1.6f));
            //AutoScrollMinSize = main_panel.Size;
            AdjustFormScrollbars(true);
            Console.WriteLine(main_panel.Height);
        }
    }
}

If anyone has an idea on why this bug is occuring, I am interested, as this really looks like a bug from the autoscroll property, maybe in 4.0.