[udaaff]

У меня так заработало:

mdm.Exception.DebugWindow.show();
//
var so:SharedObject = SharedObject.getLocal("userHighScore", "/");
if (so.data.someData == undefined) {
	mdm.Exception.DebugWindow.trace("so.data.someData  " + so.data.someData);
	so.data.someData = "asdf";
	mdm.Exception.DebugWindow.trace("so.data.someData  " + so.data.someData);
}
so.data.someData += "_X_";
so.flush();
//
mdm.Exception.DebugWindow.trace("so.data.someData  " + so.data.someData);
mdm.Exception.DebugWindow.trace("...");