Version:            (using KDE KDE 3.5.6)
Installed from:    Debian stable Packages

Reported in Debian BTS at http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=337225

When you close kontact and it has accessed read-write, even if not
written in it, a file that has more than one hard link, kontact creates
a new file at the path it has accessed, with a new inode, thus
"breaking" the hard links (their content wil not be updated anymore).

Here's my steps to reproduce the bug:

$ cat > foo.ics <<EOF
BEGIN:VCARD
CLASS:PUBLIC
FN:John Smith
N:Smith;John;;Mr;
TEL;TYPE=CELL:+123456789
VERSION:3.0
END:VCARD
EOF
$ stat -c "%i %n" *
1917526 foo.ics
$ ln foo.ics bar.ics
$ stat -c "%i %n" *
1917526 bar.ics
1917526 foo.ics
$ kontact

Add foo.ics as a new address book, read-only, quit kontact.

$ stat -c "%i %n" *
1917526 bar.ics
1917526 foo.ics
$ kontact

Remove foo.ics address book. Quit kontact.

$ stat -c "%i %n" *
1917526 bar.ics
1917526 foo.ics
$ kontact

Add foo.ics as a new address book, read-write, quit kontact.

$ stat -c "%i %n" *
1917526 bar.ics
1918815 foo.ics
1918812 foo.ics_4

OK, link's broken...

I had the same bug with my calendar, thus the bug filed on kontact. I
suspect it is a general KDE bug.