After adding a custom counter and then going to the "Configure Counters" menu option, the Spotlight application becomes unresponsive. Shutting down the application from Task Manager and then restarting the Quest Diagnostic Services can sometimes recover the Spotlight application. The Quest Diagnostic Services are not always able to restart, however and a restart of the server is required to regain processing capabilities. After the service and\or server has restarted, the custom counter is available for use. We can never add more than one custom counter at a time without going through this restart process.
The development team has replicated the problem in the current release of Spotlight on SQL Server Enterprise 8.0.1. Defect ID ST13794 has been raised for the issue and it has been submitted to development for consideration in a future release.
There is no workaround or fix available at this point.