C#-APP: I am having a problem with removing event handlers

[khalid galal]

Hi, i am having a problem with removing event handlers, it is when creating nested event handlers (an event handler raising another event handler) where a part of the code is
private void toolStripButton1_Click(object sender, EventArgs e)
{
this.MouseDown += new System.Windows.Forms.MouseEventHandler(this.Form1_ MouseDown);
}
private void Form1_MouseDown(object sender, MouseEventArgs e)
{
this.MouseUp += new System.Windows.Forms.MouseEventHandler(this.Form1_ MouseUp);
}
////////////////////////////////////////////////
so, when i say

this.MouseDown -= new System.Windows.Forms.MouseEventHandler(this.Form1_ MouseDown);

this.MouseUp -= new System.Windows.Forms.MouseEventHandler(this.Form1_ MouseUp);
////////////////////////////////////////////////
what happens is the event handler which is "this.MouseDown"
only is removed and the other event handler which is
"this.MouseUp" doesn't remove.
Thanks...