Help setting output callback with NvAPI_OGL_ExpertModeSet

I’m trying to register a GLExpert callback using the following:

NvAPI_OGL_ExpertModeSet(NVAPI_OGLEXPERT_DETAIL_ALL, NVAPI_OGLEXPERT_REPORT_ALL, NVAPI_OGLEXPERT_OUTPUT_TO_CALLBACK, MyCallback)

MyCallback is never invoked and the GLExport messages output to both the console and debugger regardless of expertOutputMask. The status code indicates that the function was successful (NVAPI_OK) and reading back the parameters using NvAPI_OGL_ExpertModeGet always has expertOutputMask as 0.

Has anyone had success setting up a callback?