In a similar context, I finally ended up replacing all of the line breaks received from richmemo with "%%" before saving the text in a string list, then replacing the "%%" pairs with line breaks on retrieving the text from the string list. This may be the same thing you're encountering with the clipboard.
I don't think, though, that the line breaks are rendered at all by richmemo under linux. It seems to be something peculiar to the Windows richmemo component. Not sure about that though.