Why does the application under windows xp not allow you to reboot the computer correctly?

Question

Windows

Given: Infokiosk with windows xp sp3, with explorer disabled (instead of shell, application software is registered in the registry). An application is installed that monitors the status of devices (com or / and usb with virtual com), problems arise with rebooting! The application is not terminated from the task manager, taskkill writes that it was completed successfully, but in fact does not terminate the application. Everything is done from under the administrator account. The registry also has values ​​for automatically closing the application on reboot. shutdown with -F -R options doesn't help either. What else can you recommend?