I am using 2.20.

Here is how to reproduce it:

1. In OwnCloud, open the files app and create a file in Notes.
2. Open it in the files app and add some content with more than one line.
3. Save it
4. In the OwnClud Notes app (>= 0.5.1) open the note and add some more lines
5. Go back into the files app and open it
6. It still looks correctly
7. Now, open khtNotes on the N9 and sync it
8. In khtNotes, open the note
9. After every added line, an empty line is visible.
10. Add a line and sync again
11. Now in the owncloud, also every line has an empty line after itself.

I think it might have something to do with the line ending.
I am usually using only \n. I know that there can issues between Linux and Windows. But in this case any editor on those systems show it correctly.

Use the attached version since in apps.owncloud.org its not approved yet.