I have just seen a massive GDI-object leakage today working with some application! 😀
The application runs on Windows XP and when the number of GDI-objects equals to the 9999, there are user-interface artifacts. So, the root cause: that application uses a timer and every time interval it allocates some GDI-resources, but does not release it. I have found the root cause by using Windows Task Manager (Handles counter column).