Removing Items from one ListBox affects another

I have three listboxes, lst, lstA, and lstB, in which lstA is an instance of lst.  The problem I have is that whenever I remove an item from lst, the same item in lstA is also removed.  I have tried assigning a different ID to lstA to no avail.  Please see my code below:
ListBox lstA = new ListBox();

lstA = lst;

lstA.ID = "new";

for ( ...