Why autosizing does not resizes a FlowLayoutPanel to a corresponding size without scrollbars

Question

I try to add some UserControls via code to a System.Windows.Forms.FlowLayoutPanel (.net 4.0).
I have set the .AutoSize and WrapContents -Property to True. I wanted to have each control in a new 'Row'.

At my Test-Form i have enough space to add several instances of my MyUserControl.
The Problem is:

For every 2nd control i add, both scrollbars appear at the FlowLayoutPanel.

Step by step:

1. Starting the application with a lot of empty space... (design mode to show flowlayoutpanel size) - but almost the same ;)

   

2. Adding the very first control:
   The red area is the flowlayoutcontrol, the blue one is my usercontrol.

   

3. Adding the 2nd control ends up in a flowlayout which have scrollbars (as i dont want)

   

4. Adding another control sizes the flowlayout pannel correctly (as i want)

   

I can go further like this. Repeatly the same problem.

Here are my codeparts:

Main-Form ctr:

PanelToUse.AutoSizeMode = AutoSizeMode.GrowAndShrink;
PanelToUse.Anchor = AnchorStyles.Top | AnchorStyles.Bottom | AnchorStyles.Left | AnchorStyles.Right;  
PanelToUse.BackColor = System.Drawing.Color.Red;                           
PanelToUse.AutoSize = true;

Behind the ADD-Button:

 var myNewBlueControl = new MyUserControl1();
 myNewBlueControl.Visible = true;
 this.PanelToUse.Controls.Add(myNewBlueControl);

Any useful suggestion? What do i miss?
Thanks in advance!!

EDIT: Here are all codeparts to reproduce this issue:

Create a new WindowsForms-Project.

• Add a new UserControl and rename this class to "MyUserControl1"

• In the MyUserControl1-Ctr add the following code:

  this.Size = new Size(410, 100); this.BackColor = Color.Blue;

• Add the following member to the Form1-Class:

  FlowLayoutPanel panelToUse;

• Add this Code to the Form1-Constructor

          this.Size = new Size(1046, 367);
          this.MaximumSize = new Size(550, 700);
  
          panelToUse = new FlowLayoutPanel();
          this.Controls.Add(this.panelToUse);
          panelToUse.WrapContents = true;
          panelToUse.Location = new Point(10, 10);
          panelToUse.AutoSizeMode = AutoSizeMode.GrowAndShrink;
          panelToUse.Anchor = AnchorStyles.Top | AnchorStyles.Bottom | AnchorStyles.Left | AnchorStyles.Right;
          panelToUse.BackColor = System.Drawing.Color.Red;
          panelToUse.AutoSize = true;
          panelToUse.AutoScroll = true;
          panelToUse.Visible = true;
  

• Than add a new Button to the very right corner and set its anchor to Bottom, Right

• In the click-eventhandler of the add-button insert this code:

  var myNewBlueControl = new MyUserControl1(); myNewBlueControl.Visible = true; this.panelToUse.Controls.Add(myNewBlueControl);