So for my tst, I took example of nms:delivery schema. It has a description field with attribute name as desc and it can contain multiline text.
So here's what I did.
Inside the Export wizard, come to Data formatting screen. On the right side you have a button to add a computed field. Please click on it.
Provide it a Label and internal name.
If you wish to replace newline characters please use the expression like I used. source.desc.replace(/(\r\n|\n|\r)/gm,""). I'm replacing the newline characters by a blank space. You can add any character of your choice.
Last step, We need to uncheck the option to export Description field. We added it to export menu so as to create our formula.
Please complete the wizard to export this in a CSV file and it should do the trick for you.
Thanks for the fast reply - using XML definitely does solve the problem, though it seems to make the output a pretty big file, which is kind of a problem in itself. If it's possible to fix the data & keep csv or tsv format, that'd be my preference, but I may resort to xml if not.
Data looks like