I was stuck the whole afternoon in debugging... finally i found something interesting...

Every time Delphi's Dynamic Array , (setLength fun) is extended, the original array cells' addresses may be changed...

Because I use TTreeView to link its Data (Pointer) to a particular cell of a dynamic array.

e.g.

  TreeView.Data:=@dynamic_array[i];
  
and 

  unfortunately, the program adds one cell to dynamic_array somewhere...
  
  setLength(dynamic_array,length(dynamic_array)+1);
  
the original cells' address are totally different, which is really confusing....

anyway, i solved this by taking the alternative...

  TreeView.Data:=Pointer(i);
  
  when i use it, i go for something like this..
  
  dynamic_array[integer(TreeView.Data)];
  
Haha, everything works out finally.