I have an issue with multi lines fields with a carddav (Davical) backend. When creating or updating a contact with multiple lines in the note field, the value gets cut off because an invalid vcard is created. To fix this I have added this line in carddav.php, line 1269:
$val = str_replace("\n", "\\n", $val);
This escapes the newlines in the value, which make sure that a valid vcard is created in Davical.
Is this something for the main branch?