I can't personally reproduce that. I suspect that you've already given your app birthday permissions (from before), so it's already available and we do use it if provided. In that regard, it is already fixed, while still using the birthday if it's available (which simplifies the registration). Since we don't ask for it, it will likely only be provided if it's public (though not even with that in my local tests).
As such, I don't think there are any changes to be made to this now.