Problems with widgets "dialog" jquery-ui 1.11

Problems with widgets "dialog" jquery-ui 1.11

Hello!
I used the version of jquery UI 1.10.4 and all was well. But recently upgraded to jquery UI 1.11 and I am having a problem with the widget "Dialog":
in my application when you click on a button, it opens a dialog box, and when the window is open I open another window. In the version of jquery UI 1.10.4 the first window became inactive, was behind the <div class="ui-widget-overlay ui front"></div>, and the second window becomes active. When you close the second window, the first again became active. In jquery UI 1.11 this effect does not occur, both Windows remain active, and a <div class="ui-widget-overlay ui front"></div> overlap each other.
Example link (jquery UI 1.11) - http://codepen.io/ppotenihin/pen/rsxnw

Example link ( jquery UI 1.10.4 ) - http://codepen.io/ppotenihin/pen/nKbsC
This is a bug or it should be?
I apologize for my English, I badly know English and I use a translator.