Problem with tooltip

Hi all,
I have a problem with tooltips.
On a ChildAppWindow a draw a schedule. The schedule shows the hirers of a 
s****ts hall. Form left to right the hours of a day, from top to bottom the

days of a week. The hirers are reprecented by different colors, for this 
RectangleObjects are drawn.
Recently I added a tooltip at moveover showing the name of the hirer.
Problem is that on about the lower 1/3 this does not work, no tooltip is 
shown. HitTest returns true however.
As all drawing is relative to the size of the window, I can draw it in any

size. Strange thing is that If I resize my screen to a smaller height, it 
all works fine.
Does somebody has any clue where to look for ?


Tia,

Erik


The Tooltip is initialized in the postinit like this:

hTooltip := CreateWindowEx( WS_EX_TOPMOST,;
      String2Psz(TOOLTIPS_CLASS),;
      NULL_PTR,;
      _OR(WS_POPUP, TTS_NOPREFIX, TTS_ALWAYSTIP , TTS_BALLOON),;
      CW_USEDEFAULT,;
      CW_USEDEFAULT,;
      CW_USEDEFAULT,;
      CW_USEDEFAULT,;
      SELF:Handle(),;
      NULL_PTR,;
      _GetInst(),;
      NULL_PTR)

SELF:AddToolTip( SELF:Handle(),4711,  "Test" )
 SendMessage( hTooltip,TTM_ACTIVATE, 1, 0)
 SendMessage(hTooltip, TTM_SETMAXTIPWIDTH, 0, 200)

 SendMessage(hTooltip, TTM_SETDELAYTIME, TTDT_AUTOPOP, 1500)
 SendMessage(hTooltip, TTM_SETDELAYTIME, TTDT_RESHOW, 1)




METHOD AddToolTip(hW AS PTR, nID AS INT, cT AS STRING) AS VOID PASCAL
CLASS 
Color_Rooster_Window

  LOCAL rc IS _winRECT
 IF hTooltip == NULL_PTR
  //? "Error"
  RETURN
 ENDIF

 GetClientRect(hW, @[EMAIL PROTECTED]
)
 ti.cbSize := _SIZEOF(_winTOOLINFO)
 ti.uFlags := TTF_SUBCLASS
 ti.hwnd := hW
 ti.hinst := _GetInst()
 ti.uId := nID
 ti.rect.left := rc.left
 ti.rect.top := rc.top
 ti.rect.right := rc.right
 ti.rect.bottom := rc.bottom
 ti.lpszText := String2Psz("Testdertest") //LPSTR_TEXTCALLBACK
 SendMessage(hTooltip, TTM_ADDTOOL, 0L, LONG(_CAST, @[EMAIL PROTECTED]
))
 RETURN

And this is the MouseMove Method
METHOD MouseMove(oMouseEvent) CLASS Color_Rooster_Window
   LOCAL nButtonID AS INT
   LOCAL xPos, yPos AS INT
   LOCAL cAllText   AS STRING

   nButtonID := IIF(oMouseEvent == NULL_OBJECT, 0, oMouseEvent:ButtonID)

   SUPER:MouseMove(oMouseEvent)

   xPos := oMouseEvent:Position:x
   yPos := oMouseEvent:Position:y
      IF SELF:Hittest( xPos, yPos, @[EMAIL PROTECTED]
  )
          //  returns true, cAllText contains a name so everything is fine
          //  but the tooltip is not shown on the lower part of the screen
          ti.lpszText := String2Psz( cAllText  )
         SendMessage(hTooltip, TTM_ADDTOOL, 0L, LONG(_CAST, @[EMAIL PROTECTED]
))
         SendMessage(hTooltip, TTM_UPDATETIPTEXT, 0L, LONG(_CAST, @[EMAIL PROTECTED]
))
      ELSE
         ti.lpszText := String2Psz( "")
         SendMessage(hTooltip, TTM_DELTOOL, 0L, LONG(_CAST, @[EMAIL PROTECTED]
))
       ENDIF

   RETURN NIL