Index: objectinspector.pp
===================================================================
--- objectinspector.pp	(revision 59606)
+++ objectinspector.pp	(working copy)
@@ -312,6 +312,7 @@
     FKeySearchText: string;
     FHideClassNames: Boolean;
     FPropNameFilter : String;
+    FPaintRc: TRect;
 
     // hint stuff
     FLongHintTimer: TTimer;
@@ -435,6 +436,7 @@
   protected
     procedure CreateParams(var Params: TCreateParams); override;
     procedure CreateWnd; override;
+
     procedure Notification(AComponent: TComponent; Operation: TOperation); override;
 
     function DoMouseWheel(Shift: TShiftState; WheelDelta: Integer; MousePos: TPoint): Boolean; override;
@@ -701,6 +703,8 @@
     FOnShowOptions: TNotifyEvent;
     FOnUpdateRestricted: TNotifyEvent;
     FOnViewRestricted: TNotifyEvent;
+    FLastTreeSize: TRect;
+
     // These event handlers are assigned at run-time, no need for default published section.
     procedure ComponentTreeDblClick(Sender: TObject);
     procedure ComponentTreeGetNodeImageIndex(APersistent: TPersistent; var AIndex: integer);
@@ -1218,7 +1222,7 @@
     if TopY > ATopMax then
       TopY := ATopMax;
     ScrollInfo.nPos := TopY;
-    ShowScrollBar(Handle, SB_VERT, True);
+  //  ShowScrollBar(Handle, SB_VERT, True);
     SetScrollInfo(Handle, SB_VERT, ScrollInfo, True);
   end;
 end;
@@ -1277,6 +1281,7 @@
 begin
   inherited CreateWnd;
   // handle just created, set scrollbar
+  ShowScrollBar(Handle, SB_VERT, True);
   UpdateScrollBar;
 end;
 
@@ -2751,7 +2756,7 @@
 procedure TOICustomPropertyGrid.SetTopY(const NewValue:integer);
 var
   NewTopY, d: integer;
-  r: TRect;
+//  r: TRect;
   f: UINT;
 begin
   NewTopY := TopMax;
@@ -2760,7 +2765,7 @@
   if NewTopY < 0 then
     NewTopY := 0;
   if FTopY<>NewTopY then begin
-    r := ClientRect;
+//    r := ClientRect;
     f := SW_INVALIDATE;
     d := FTopY-NewTopY;
     // SW_SCROLLCHILDREN can only be used, if the active editor is not
@@ -2770,7 +2775,8 @@
        ( (d < 0) and (FCurrentEdit.Top <  Height - FCurrentEdit.Height) )
     then
       f := f + SW_SCROLLCHILDREN;
-    if not ScrollWindowEx(Handle,0,d,@r,@r,0,nil, f) then
+//    if not ScrollWindowEx(Handle,0,d,@r,nil,0,nil, f) then
+    if not ScrollWindowEx(Handle,0,d,nil,nil,0,nil, f) then
       Invalidate;
     FTopY:=NewTopY;
     UpdateScrollBar;
@@ -2902,8 +2908,13 @@
       {$ENDIF}
       end;
       //debugln('TOICustomPropertyGrid.AlignEditComponents A ',dbgsName(FCurrentEdit),' ',dbgs(EditCompRect));
-      if FCurrentEdit.BoundsRect <> EditCompRect then
+      if ( ( (FCurrentEdit.BoundsRect.Bottom >= 0) and (FCurrentEdit.BoundsRect.Top <= Height) ) or
+           ( (EditCompRect.Bottom >= 0) and (EditCompRect.Top <= Height) ) ) and
+         ( FCurrentEdit.BoundsRect <> EditCompRect )
+      then begin
+//DebugLn(['            ',FCurrentEdit.BoundsRect.Top , ' >> ', EditCompRect.Top]);
         FCurrentEdit.BoundsRect := EditCompRect;
+      end;
     end;
   end;
 end;
@@ -3067,6 +3078,8 @@
 begin
   CurRow := Rows[ARow];
   FullRect := RowRect(ARow);
+  if (FullRect.Bottom < FPaintRc.Top) or (FullRect.Top > FPaintRc.Bottom) then
+    exit;
   NameRect := FullRect;
   ValueRect := FullRect;
   Inc(FullRect.Bottom, FRowSpacing);
@@ -3173,6 +3186,9 @@
   SpaceRect: TRect;
   GutterX: Integer;
 begin
+  FPaintRc := Canvas.ClipRect;
+  debugln([' PAINT ',FPaintRc.Top, ' - ', FPaintRc.Bottom, ' / ', FPaintRc.Bottom-FPaintRc.Top]);
+
   BuildPropertyList(true);
   if not PaintOnlyChangedValues then
   begin
@@ -5616,8 +5632,12 @@
 procedure TObjectInspectorDlg.Resize;
 begin
   inherited Resize;
-  if Assigned(ComponentTree) then
+  // BUG: resize gets called, even if nothing changed
+  if Assigned(ComponentTree) and (FLastTreeSize <> ComponentTree.BoundsRect) then begin
+  debugln('Resize dlg');
     ComponentTree.Invalidate;  // Update Scrollbars.
+    FLastTreeSize := ComponentTree.BoundsRect;
+  end;
 end;
 
 procedure TObjectInspectorDlg.ComponentTreeModified(Sender: TObject);