Reported by @shaunandrews:

I'm getting an error. Looks like something happening with Jetpack: Warning: Invalid argument supplied for foreach() in /Users/shaunandrews/Sites/WordPress/wp-content/plugins/jetpack/modules/widget-visibility/widget-conditions.php on line 249

Either the Jetpack plugin is not extending widgets properly, or the Widget Customizer is not adequately setting up the environment for rendering widget controls in the customizer.