From Thibault Genessay, "On Windows, when setting a cursor through

osgViewer::GraphicsWindow::setCursor() the new cursor type is recorded
but not applied until windows sends another WM_SETCURSOR message. This
delays the application of the cursor to the next mouse event.

The attached file fixes this by setting the new cursor with a call to
::SetCursor() immediately.
"

src/osgViewer/GraphicsWindowWin32.cpp

@@ -1847,6 +1847,9 @@ void GraphicsWindowWin32::setCursor( MouseCursor mouseCursor )
 
     _currentCursor = newCursor;
     _traits->useCursor = (_currentCursor != NULL);
+
+    if (_mouseCursor != InheritCursor)
+        ::SetCursor(_currentCursor);
 }
 
 HCURSOR GraphicsWindowWin32::getOrCreateCursor(MouseCursor mouseCursor)