I can also attest that this happens on my machine with nvidia-settings version 337.19. Xorg crashes and I get back to my display manager as the OP mentioned. Querying individual attributes seems to work correctly.
As towo mentioned, a manually compiled version of nvidia-settings-334.21 from the source here does not exhibit this issue. Maybe it’s related to the addition of the new overclocking attributes that are available in the 337 version.