Its not a bug. Microsoft has requirements as to how hardware interfaces with software..and in this case, because of their strict code for stability and such in a Windows NT based system, they don't allow the hardware to pump up the refresh rate higher than 60htz in games/screensavers/etc so that a monitor wouldn't get damaged if it switched to another resolution during a DX call.
I read that on the web in another forum hehe
Anyways.. yeah, setting the refresh rate with DXDIAG fixes DirectX, but OpenGL will still be at 60htz. Use the mentioned Nvidia Refresh Rate Fix program to correct all scenarios.