Memory of unreferenced Form not freed - garbage-collection

Question

I have created a simple test-program with two Forms. One containing a button to start the procedure and on containing only an image (or in another testcase a byte[]). Both contain a timer to allow the rendering of the forms.
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
timer1.Interval = 0;
}
private void button1_Click(object sender, EventArgs e)
{
timer1.Enabled = true;
}
private void timer1_Tick(object sender, EventArgs e)
{
// Instantiate and show Form2
timer1.Enabled = false;
var form2 = new Form2();
form2.ShowDialog();
// Dispose, force Collect and show (estimated) memory usage
form2.Dispose();
GC.Collect();
System.Diagnostics.Debug.WriteLine(GC.GetTotalMemory(true));
timer1.Enabled = true;
}
}
The other Form only closes itself (there is an PictureBox in the .designer-Part):
public partial class Form2 : Form
{
// Alternative test
// private byte[] bytes;
public Form2()
{
InitializeComponent();
timer1.Interval = 0;
timer1.Enabled = true;
//bytes = new byte[1024*1024];
}
private void timer1_Tick(object sender, EventArgs e)
{
this.DialogResult = DialogResult.Ignore;
}
}
The Point is: it doesn't matter what exactly is in Form2: the memory usage rises and at one point I'll get an OutOfMemoryException (or in case of the PictureBox a System.Exception ending in
at Microsoft.AGL.Common.MISC.HandleAr(PAL_ERROR ar)
at System.Drawing.Bitmap._InitFromMemoryStream(MemoryStream mstream)
but that seems to be an OutOfMemoryException in a native call which is not thrown properly.)
I don't understand why. There is no reference left to the old instance of Form2, I call Dispose and yet the memory is not released.
I use CF 3.5 for this.

Answer 1

Ok, multiple things were at work here:
The event handler for the Tick-event held an implicit reference to the form.
The timer1_Tick needs a reference to the form. As long as there is a reference to the form in the timer and a reference in the form to the pointer, the GC (at least the CF one, I did't test this on the regular Framework) cannot free the memory.
The components where not disposed.
It seems it isn't enough to call Dispose on the form. I also had to call Dispose on the Timer to free all of its memory. This is a bug.
public partial class Form2 : Form
{
private byte[] bytes;
public Form2()
{
InitializeComponent();
timer1.Interval = 0;
timer1.Enabled = true;
bytes = new byte[1024 * 1024];
}
private void timer1_Tick(object sender, EventArgs e)
{
this.DialogResult = DialogResult.Ignore;
this.timer1.Tick -= timer1_Tick;
this.timer1.Dispose();
this.mainMenu1 = null;
}
}