WPF richtextbox no line break in first line?

Question

I experienced a weird bug and am unable to solve it.

To reproduce:

1. Create new wpf project

2. Add richtextbox, name it e.g. "rtb"

3. Append a text with line break at the end 3 times. For example

rtb.AppendText("lol\n");
rtb.AppendText("lol\n");
rtb.AppendText("lol\n");

4. Now start the application. Notice how everything works fine and there are three lines saying "lol".

5. Now clear the richtextbox before appending the lines:

rtb.Document.Blocks.Clear();
rtb.AppendText("lol\n");
rtb.AppendText("lol\n");
rtb.AppendText("lol\n");

6. Start the application again. Notice that the output is no longer

   lol

   lol

   lol

but this time

   lollol

 

   lol

so essentially the "\n" for the first "lol" was added after the next "lol", lol?

Do you know what's going on because I don't. I'd expect it to output

   lol

   lol

   lol

and I don't see why clearing the text content makes the richtextbox behave like this. I guess it's a bug but I don't understand why it's happening or how can I solve this.

 

It can't be because of "rtb.Document.Blocks.Clear()" as I've tried other methods for clearing the richtextbox as well, like

 

rtb.SelectAll();
rtb.Selection.Text = "";

and other approaches. However, none of them afterwards printed the text correctly. Now in this simple scenario, doing

rtb.Document.Blocks.Clear();
rtb.AppendText("lol\nlol\nlol\n");

(writing all 'lol's at once) actually does fix the issue. However I obviously don't just print out lol, but I have to call "AppendText" multiple times, resulting in incorrect output. Any ideas? Or where should I submit a bug report? Thanks.