Hello,
I have a form that I don't want to display the title bar for. The way
I've implemented this is to to remove the WS_DLGFRAME style flag.
However, when this form is minimized and then restored, it is restored
to the wrong size. The height of the form increases 19 pixels (height
of a title bar on my computer) with every minimize/restore.

Can someone shead any light on this?

I've attached an example program. To reproduce, just create a standard
windows forms project, paste the code, and add a button to the form
whose click handler you connect to the button1_Click method.

public partial class Form1 : Form
{
 public Form1()
 {
    InitializeComponent();
 }

 // Attach this to a button click event for a button on the form
 private void button1_Click(object sender, EventArgs e)
 {
    if (IsStyleFlagSet(this.Handle, WS_DLGFRAME))
    {
       // Remove caption bar
       SetStyleFlag(this.Handle, WS_DLGFRAME , false);
       // Repaint NC area
       SetWindowPos(this.Handle, IntPtr.Zero, 0, 0, 0, 0,
SWP_FRAMECHANGED |  SWP_NOSIZE | SWP_NOMOVE | SWP_NOZORDER);
   }

   // Get my current client size
  Size prevSize = this.ClientSize;

  // Minimize and restore me
  this.WindowState = FormWindowState.Minimized;
  this.WindowState = FormWindowState.Normal;

  // Get my client size now
  Size currSize = this.ClientSize;

  if (currSize == prevSize)
    MessageBox.Show("Size was equal! :-) ");
  else
    MessageBox.Show(string.Format("Size was not equal! :-(. Before:
{0}, After: {1}", prevSize, currSize));

}

 // Style constants
 internal const int GWL_STYLE = (-16);

 internal const int WS_DLGFRAME = 0x00400000;
 internal const int WS_BORDER = 0x00800000;
 internal const int WS_CAPTION = WS_BORDER | WS_DLGFRAME;

 // SetWindowPos Flags
 internal const int SWP_NOSIZE = 0x0001;
 internal const int SWP_NOMOVE = 0x0002;
 internal const int SWP_NOZORDER = 0x0004;
 internal const int SWP_NOACTIVATE = 0x0010;
 internal const int SWP_FRAMECHANGED = 0x0020;
 internal const int SWP_NOOWNERZORDER = 0x0200;

 [DllImport("user32.dll")]
 static extern int SetWindowLong(IntPtr hWnd, int nIndex, int
dwNewLong);

 [DllImport("user32.dll", SetLastError = true)]
 static extern int GetWindowLong(IntPtr hWnd, int nIndex);

 [DllImport("user32")]
 internal static extern int SetWindowPos(IntPtr hWnd, IntPtr
hWndInsertAfter, int X, int Y, int cx, int cy, uint uFlags);

 internal static bool IsStyleFlagSet(IntPtr handle, int styleFlag)
 {
   return (GetWindowLong(handle, GWL_STYLE) & styleFlag) == styleFlag;
 }

 internal static void SetStyleFlag(IntPtr handle, int dwNewLong, bool
set)
 {
   int style = GetWindowLong(handle, GWL_STYLE);

   if (set)
     style |= dwNewLong;
   else
     style &= ~dwNewLong;

   SetWindowLong(handle, GWL_STYLE, style);
 }
}