Formatted Text: How to change the LineHeight property of a FormattedText? [has sample program]

Here's how my code looks like:

string text = "The quick brown fox jumps over the lazy dog";

double fontSize = 18;
FontFamily font = new System.Windows.Media.FontFamily("Arial");
FlowDirection flowDirection = FlowDirection.LeftToRight;

			
FormattedText formattedText = new FormattedText(
	text,
	CultureInfo.CurrentCulture,
	flowDirection,
	new Typeface(font.ToString()),
	fontSize,
	Brushes.Black);

txtBeforeChangingLineHeight.Text = formattedText.Height.ToString();

formattedText.LineHeight = 2;

txtAfterChangingLineHeight.Text = formattedText.Height.ToString();

formattedText.LineHeight = 0;

txtLineHeightBackToZero.Text = formattedText.Height.ToString();

This is inside a Click Event Handler. And here is its output when the Event Handler is fired:

Click here for screenshot of output

My problem about this is that when I changed the LineHeight property of the FormattedText, it also changes the Height property of the FormattedText. For example, if the value offormattedText.Height is equal to 20.3, then I changed the value offormattedText.LineHeight to 2, the value of formattedText.Heightwill become 2 as well.

Then when I set the formattedText.LineHeight property back to0 (which is its original value), the value of formattedText.Heightbecomes 20.3 again.

It seems that when the value of formattedText.LineHeight  is set to a value other than zero, then the value of formattedText.Heightfollows whatever value formattedText.LineHeight has.

I have two questions:

1. Why is that if i set the FormattedText's LineHeight property to a value other than zero, the said FormattedText's Height property also changes to the value of its LineHeight property?

2. How to properly set the LineHeight of the FormattedText?

By properly, I mean that the LineHeight can be set to a value other than zero and the Height will not have the same value as the  LineHeight.

Please take a look at my sample program to see what I am talking about:

Click here for the sample program