Cause if you read the release notes for kde here http://www.linuxmint.com/rel_daryna_kde.php
It has lengthy instructions for how to install with a preserved /home partition. This problem I assume is somehting that the regular linux mint release wouldn't have an issue with as neither ubuntu/kubuntu have this problem, Would I be right.
from the link
Install with an old home partition
This is what I do, a lot.
* Boot off the live DVD.
* Start the install.
* At the partitioning screen choose manual.
* Format the old / partition, now called /media/sda?.
* Set the old / partition to be the new /.
* Continue to the end and start the install.
* After the install has finished reboot the system.
* Open a terminal window to setup your old /home partition.
* Check your partitions
* df -h
* Check your old /home partition for home directories.
* ls /media/sda?
* Un-mount your old /home partition.
* sudo umount /media/sda?
* Update your /etc/fstab file to mount your old /home at boot.
* sudo vi /etc/fstab (or use another editior)
* change the /home partiton from /media/sda? to /home
* save and exit
* Reboot to have your old /home back again.
* Rember if you want to reset an applications config or KDE's, delete the application's hidden config file/directory in you home directory. eg rm -rf /home/boo/.kde
* your sound will no longer work. To fix open up kmix, check your output is not muted or the level is set to low and check the PCM level (I had to nearly max mine out).