Thank you for the research. The problem is indeed that \v is getting treated as a line separator.  That is an intentional design choice, see:

https://bugs.python.org/issue12855

It would seem to have some surprising implications for CSV parsing.  E.g. if someone embeds a \v character in a quoted field, parsing the file using codecs.getreader() will cause the field to be split across two rows.

Someone else has run into the same issue:

https://www.enigma.com/blog/the-secret-world-of-newline-characters

I'm not sure anything should be done.  Perhaps we should do something to reduce that chances that people trip over this issue.  E.g. if I want to parse a file containing Unicode text with the CSV module, how do I do it while allowing \v characters (or other new-line like characters other than \n) within fields?