To reproduce:
- Add RadRichTextBox and a button to a blank form.
- Add some text with couple of new lines in the middle of it. 
- Create a context menu with a copy command in it and assign it to the richtextbox.
- Select some of the text and copy it via the context menu item then just click the button.
- You will notice that this is causing wrong layout of the text.

Resolution: 
This issue is addressed in the new version of the control - RadRichTextEditor. Please use the new control instead the RadRichTextBox.