addWindowContent with button now working properly

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Create window && create a button (or any class that extends from it)
2. add the button to the window with window.addWindowContent(button)

What is the expected output? What do you see instead?
The button does not show up on screen, while it should work as when using 
addChild

What version of the product are you using? On what operating system?
tonegodGui from svn r637 - linux 64bit

Please provide any additional information below.
Commenting out the line:305 in Window class seam to solve the issue :

//      contentArea.addClippingLayer(contentArea);

Original issue reported on code.google.com by [email protected] on 26 Feb 2015 at 8:40

[GoogleCodeExporter]

I forgot to mention that the button is attach to a label, who is attach then to 
the window :
 - window > label > button

Original comment by [email protected] on 26 Feb 2015 at 8:49