What is $rootscope.$$phase = null?

Question

I use kendo ui and angular.js in my application. When i do some actions like hover or click event on some elements i see that other elements simply disappear. I debug it and see in angular.js file

$rootscope.$$phase = null;

and then the elements disappear.

What is this:

$rootscope.$$phase = null;

and how to prevent it?