[PROBLEM] Set Button HeightRequest

I have this code:

loginBox_bttLogin = new Button
            {
                HeightRequest = 30,
                Text = "ĐĂNG NHẬP",
                TextColor = Color.White,
                FontAttributes = FontAttributes.Bold,
                BackgroundColor = Color.FromHex("#006fb4")
            };

But when i run app on android os 5.0, it ok. on android os 4.4, it have problem for text inside button.
Sorry my english not good, thanks for read.

OS: 4.4 API 19

OS: 5.0 API 21