Works for me...
Might want to check out the following bug fixes, change your Include with these and see if that works.
I tested with a large amount of data in the listview(s) with the code below.
#include <GUIConstants.au3>
#include <GuiListView.au3>
GUICreate("listview items", 460, 350, 100, 200, -1, $WS_EX_ACCEPTFILES)
GUISetBkColor(0x00E0FFFF); will change background color
$listview = GUICtrlCreateListView("col1 ", 10, 10, 200, 150);,$LVS_SORTDESCENDING)
For $x = 1 To 1000
GUICtrlCreateListViewItem("item" & $x, $listview)
Next
GUICtrlSetState(-1, $GUI_DROPACCEPTED); to allow drag and dropping
$listviewB = GUICtrlCreateListView("col2 ", 10, 180, 200, 150);,$LVS_SORTDESCENDING)
$itemB1 = GUICtrlCreateListViewItem("item2", $listviewB)
$itemB2 = GUICtrlCreateListViewItem("item1", $listviewB)
$itemB3 = GUICtrlCreateListViewItem("item3", $listviewB)
For $x = 4 To 100
GUICtrlCreateListViewItem("item" & $x, $listviewB)
Next
$listviewC = GUICtrlCreateListView("col3 ", 220, 10, 200, 150);,$LVS_SORTDESCENDING)
$btn_compare = GUICtrlCreateButton("Compare", 260, 190, 120, 25)
GUISetState()
Do
$msg = GUIGetMsg()
Select
Case $msg = $btn_compare
For $x = 0 To _GUICtrlListViewGetItemCount($listview) - 1
$found = False
$s_item1 = _GUICtrlListViewGetItemText($listview, $x, 0)
For $y = 0 To _GUICtrlListViewGetItemCount($listviewB) - 1
$s_item2 = _GUICtrlListViewGetItemText($listviewB, $y, 0)
If StringUpper($s_item1) = StringUpper($s_item2) Then
$found = True
ExitLoop
EndIf
Next
If Not $found Then GUICtrlCreateListViewItem($s_item1, $listviewC)
Next
Case $msg = $listview
MsgBox(0, "listview", "clicked=" & GUICtrlGetState($listview), 2)
EndSelect
Until $msg = $GUI_EVENT_CLOSE