I am facing exactly the problem mentioned in these links:
http://code.google.com/p/android/issues/detail?id=2373
http://groups.google.com/group/android-devel
Similar solution for Xamarin.Android:
if (!IsTaskRoot) { string action = this.Intent.Action; if (this.Intent.HasCategory(Intent.CategoryLauncher) && !string.IsNullOrEmpty(this.Intent.Action) && action == Intent.ActionMain) { Finish(); return; } }