GUI blinks on button clicks

#include <GUIConstantsEx.au3>

Global $tab[6], $button[6]

Main()

Func Main()
$MainGUI = GUICreate("Main", 645, 568)
GUISetBkColor(0xFFFFFF)
GUICtrlCreatePic(@ScriptDir & "\img_bg_gray.bmp", 0, 0, 645, 568)
GUICtrlSetState(-1, $GUI_DISABLE)

$tabpane = GUICtrlCreateTab(10, 10, 200, 100)

$tab[0] = GUICtrlCreateTabItem("tab1")
$Label0 = GUICtrlCreateLabel("Summary1", 320, 110, 209, 24)
GUICtrlSetFont(-1, 16, 800, 0, "Arial")

$tab[1] = GUICtrlCreateTabItem("tab2")
$Label1 = GUICtrlCreateLabel("Summary2", 320, 110, 209, 24)
GUICtrlSetFont(-1, 16, 800, 0, "Arial")

$tab[2] = GUICtrlCreateTabItem("tab3")
$Label2 = GUICtrlCreateLabel("Summary3", 320, 110, 209, 24)
GUICtrlSetFont(-1, 16, 800, 0, "Arial")

$tab[3] = GUICtrlCreateTabItem("tab4")
$Label3 = GUICtrlCreateLabel("Summary4", 320, 110, 209, 24)
GUICtrlSetFont(-1, 16, 800, 0, "Arial")

$tab[4] = GUICtrlCreateTabItem("tab5")
$Label4 = GUICtrlCreateLabel("Summary5", 320, 110, 209, 24)
GUICtrlSetFont(-1, 16, 800, 0, "Arial")

$tab[5] = GUICtrlCreateTabItem("tab6")
$Label5 = GUICtrlCreateLabel("Summary6", 320, 110, 209, 24)
GUICtrlSetFont(-1, 16, 800, 0, "Arial")

GUICtrlCreateTabItem("") ; end tabitem definition

$button[0] = GUICtrlCreateButton("Tab 1", 15, 20, 130, 39)
$button[1] = GUICtrlCreateButton("Tab 2", 15, 60, 130, 39)
$button[2] = GUICtrlCreateButton("Tab 3", 15, 100, 130, 39)
$button[3] = GUICtrlCreateButton("Tab 4", 15, 140, 130, 39)
$button[4] = GUICtrlCreateButton("Tab 5", 15, 180, 130, 39)
$button[5] = GUICtrlCreateButton("Tab 6", 15, 220, 130, 39)

GUICtrlSetState($tabpane, $GUI_HIDE) ;<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

GUISetState()

; Run the GUI until the dialog is closed
While 1
$msg = GUIGetMsg()
Switch $msg
Case $GUI_EVENT_CLOSE
Exit
Case $button[0]
GUICtrlSetState($tab[0], $GUI_SHOW)
Case $button[1]
GUICtrlSetState($tab[1], $GUI_SHOW)
Case $button[2]
GUICtrlSetState($tab[2], $GUI_SHOW)
Case $button[3]
GUICtrlSetState($tab[3], $GUI_SHOW)
Case $button[4]
GUICtrlSetState($tab[4], $GUI_SHOW)
Case $button[5]
GUICtrlSetState($tab[5], $GUI_SHOW)
EndSwitch
WEnd
EndFunc ;==>Main