Backspace stops designer
Tested at the Windows platform. If you hit the backspace key, you will see the designer splash screen and the designer is not working anymore. The only way to end the designer is to hit the close button inside of the screen.
Known issue that will be fixed in the next update.
This update has been pushed out in Build Version: xds-126.96.36.199.
You can determine what current build version you are running by going to Help -> About.