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 toolStripButton 1_Click(object sender, EventArgs e)
{
this.MouseDown += new System.Windows. Forms.MouseEven tHandler(this.F orm1_MouseDown) ;
}
private void Form1_MouseDown (object sender, MouseEventArgs e)
{
this.MouseUp += new System.Windows. Forms.MouseEven tHandler(this.F orm1_MouseUp);
}
////////////////////////////////////////////////
so, when i say

this.MouseDown -= new System.Windows. Forms.MouseEven tHandler(this.F orm1_MouseDown) ;

this.MouseUp -= new System.Windows. Forms.MouseEven tHandler(this.F orm1_MouseUp);
////////////////////////////////////////////////
what happens is the event handler which is "this.MouseDown "
only is removed and the other event handler which is
"this.Mouse Up" doesn't remove.
Thanks...