merge and hard links

I would like to see an improvement along the following lines:

I have a set of hard links, because the content of the files should always be the same, and when I delete a file, it shouldn't affect the other places. (in other words, hardlinks work perfectly for me).

Now when I use kdiff3 and merge the file (at one of the hard links), when I save the merge result (save as), the hard link is moved to file.orig and the new file is not a hard link. In other words, the change is not propagated through the existing hardlinks, instead, a new file is created.

This is different than the standard (linux) cp works; e.g. the following sequence works as I would expect:

echo date > f1.txt
ln f1.txt f2.txt
ln f1.txt f3.txt
ln f1.txt f4.txt

echo NEW-date > f5.txt

and when I then do

cp f5.txt f4.txt

then F[1-3].txt get updated as well.

Why is kdiff3 using something different than cp when saving a merge result on a hardlink? (I use kdiff3 within mercurial but I verified that this behaviour comes from kdiff3, not mercurial). At least I would like to see an option in the settings to get this behaviour (that it behaves like cp, and not creating a file.orig)!