OK, so I investigate a little and the problem is related to TextField.
Each time I create a new Textfield instance...
var txt:starling.text.TextField = new starling.text.TextField(txtWidth, txtHeight, txtLabel, txtEmbeddedFont, txtFontSize, txtColor);
...the app restarts and goes background.
Maybe it is related to the embedded status of the font but I must do further tests to confirm.
the font is embedded like this in a static Class:
[Embed( source = "../../lib/fonts/tahoma.ttf",
mimeType = "application/x-font-truetype",
embedAsCFF = "false",
fontFamily = "Tahoma")]
private static const Tahoma:Class;
Anyone has the same issue with TextField and/or embedded fonts ?