The WM_MOUSEWHEEL message is specified to have absolute screen

windows/message.c

@@ -375,7 +375,9 @@ static void process_raw_mouse_message( MSG *msg, BOOL remove )
 
     pt = msg->pt;
     /* Note: windows has no concept of a non-client wheel message */
-    if (hittest != HTCLIENT && msg->message != WM_MOUSEWHEEL)
+    if (msg->message != WM_MOUSEWHEEL)
+    {
+        if (hittest != HTCLIENT)
         {
             msg->message += WM_NCMOUSEMOVE - WM_MOUSEMOVE;
             msg->wParam = hittest;
@@ -384,7 +386,9 @@ static void process_raw_mouse_message( MSG *msg, BOOL remove )
         {
             /* coordinates don't get translated while tracking a menu */
             /* FIXME: should differentiate popups and top-level menus */
-        if (!(info.flags & GUI_INMENUMODE)) ScreenToClient( msg->hwnd, &pt );
+            if (!(info.flags & GUI_INMENUMODE))
+                ScreenToClient( msg->hwnd, &pt );
+        }
     }
     msg->lParam = MAKELONG( pt.x, pt.y );
 }