Wpf richtextbox - losing line breaks on copy/paste operation

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C#

I needed a text control that provided a one-way copy to clipboard function while also being able to format specific lines and part of lines so I tried the RichTextBox. This is working pretty well. The problem is when I perform a copy and paste operation to the clipboard. All the the line breaks ('\n') are removed and the copied text is run together on a single line.

For instance:
This is line 1.
This is line 2.
This is line 3.

Becomes:
This is line 1.This is line2.This is line 3.

The text of the RichTextBox is being populated from code-behind due to the very dynamic nature of what is being displayed.

// example
var myDoc = new FlowDocument();

foreach (MyDataObject dObj in dataFromDatabase)
{
  var para = new Paragraph();
  para.Inlines.Add(new Run(dObj.DataPoint1.ToString()));
  if (dObj.DataPoint2 > 3)
  {
    para.Inlines.Add(new Run("\nThis exceeds reporting threshold for blah, blah, blah,...")); // \n or \r it doesn't matter, they are both removed in copy/paste
  }
  // and other lines as required in the program logic
  
  myDoc.Blocks.Add(para);
}

myRichTextBox.Document = myDoc;

What I have tried:

I have searched the internet for how to prevent this but all I have found is substituting a carriage return ('\r') for the line break but it also did not work.