Had one contact in a separate file, was using "dir address book" in kontact to access the data. Upon modifying the data, the name changed from "123" to some cryptic string (unique identifier?). Also the revision-tag that was placed in the original file was removed.
The original files have been created by syncing a mobile phone (using msynctool) to a vcard30-storageformat into a directory.

anonymised form of the original vcard:
BEGIN:VCARD
VERSION:3.0
ADR;TYPE=HOME:;;abc;abc;;12345;abc
ADR;TYPE=WORK:;;abc;abc;;12345;abc
EMAIL;TYPE=INTERNET:abc
N:Paul;Mueller;;;
ORG:abc;
REV:20070731T124117Z
TEL;TYPE=WORK:+99 (123) 456789
TEL;TYPE=CELL:+99 (234) 567890
URL:http://www.example.com/
END:VCARD

and of the resulting vcard after editing/saving the entry in kontact:
BEGIN:VCARD
ADR;TYPE=HOME:;;abc;abc;;12345;abc
ADR;TYPE=WORK:;;abc;abc;;12345;abc
CLASS:PUBLIC
EMAIL:abc
FN:Paul Mueller
N:Paul;Mueller;;;
ORG:abc
REV:2008-12-28T14:53:20Z
TEL;TYPE=WORK:+99 (123) 456789
TEL;TYPE=CELL:+99 (234) 567890
UID:2WuGkU8Odu
URL:http://www.example.com/
VERSION:3.0
END:VCARD