I hope this will be of help. Following on from this thread I've done a bit of digging around and it does seem that user qwerty seems to make it across to an installed system in a number of places:-

The libre-office file is one. If you look in ./~config/libreoffice/4
there's a .lock file for qwerty that presumably was created when the
system was being tested and got left behind on ISO build.
[Lockdata]
User=qwerty
Host=qwerty-PC
Stamp=968730D5B2BEB2561E8B37CF517AEE69
Time=Wed Feb 25 11:58:07 2015
IPCServer=true

I also found qwerty when looking at the bookmarks for file manager in ./~config/gtk-3.0/ as none of the bookmarks were working properly

.~/.config/font-manager/preferences.ini
[Font Folder]
folder = /home/qwerty/.fonts

.~/.config/fontconfig/ - multiple pointers to invalid location
 <include ignore_missing="yes">/home/qwerty/.config/font-manager/conf.d</include>

~/.guayadeque/guayadeque.conf plus others
Path0 value="/home/qwerty/Music"/

~/.config/syncthing/config.xml
<folder id="default" path="/home/qwerty/Sync" ...

Slighty off topic, dmesg also revealed that conkyrc was pointing to an invalid entry for Trash which was messing up the accuracy of the display.

There are others. These are all relatively easy to fix - but if something is not working as you expect it can be a pain if you don't know where to look - perhaps something to consider for next release? Maybe a script to convert incorrect entries for current users?

Thank you