@prologic@twtxt.net make the text field twt.LiteralText() instead of twt.FormatText() and you should be good. 
@prologic@twtxt.net Its not FormatText stripping out the lines. That formats with \n newlines so when unmarshalling it tries to parse the text and sees that as the end of twt. LiteralText keeps the newlines as \u2028