Thank you for reporting this problem to us, I managed to reproduce it on my side. Your request has been linked to the appropriate issue. We will let you know once it is resolved.
As a temporary workaround, you can remove LineFeed characters from your document. For example, see the following code:
Document doc = new Document(@"Test001\in.docx");
doc.Range.Replace(ControlChar.LineFeed, "", false, false);
Thanks for your request. Unfortunately, I cannot provide you an estimate right now. Our developers will analyze the issue and we get back to you with more details.