Label YAlign property does not work when changing font size in iOS

The YAlign property does not work when I change the font size of a label in iOS. In Android it works fine.

Is this a known bug? Does someone know a workaround for this issue?

Used setting:
myLabel.VerticalOptions = LayoutOptions.FillAndExpand;
myLabel.XAlign = TextAlignment.Center;

For the default font size it works as expected.

Used Xamarin.Forms version:
1.4.0.6341 stable