SteamVR beta has been updated with the following changes.

If you encounter issues with this update, please post in the SteamVR Bug Report forum. If possible, please include a system report to aid in tracking down your issue. Replies to this post are not tracked for bug reporting purposes. Please use the forum linked above to report issues.

SteamVR:

• Enabled desktop view for monitors attached to a non-HMD GPU.
  
• Added raw input sanity checking for physical mouse override on desktop view.