ui-dialog overlay background not showing

[graphicsxp]

I have found an issue with the dialog control. The overlay background does not show up after navigating to a different view. That's if the dialog has been opened at least once.

To reproduce the issue, use the plunkr of issue #335 : http://plnkr.co/MhYssd1GiOx1d1YwOyf0

And follow this steps:

1. Click 'Second View'
2. Click the button 'Finally click me for a message box that dissapears when pressing back'
3. Press back button of browser
4. Click 'First View'
5. Click 'Second View'
6. Click one of the two buttons to open a message box, and the overlay background is gone.

[pkozlowski-opensource]

It will be solved via #441