Systemback changes default session and autologon

I have created a live Image of Xubuntu 16.04 LTS with systemback, which has a custom default session, an script to set the hostname and a custom autologon. When I boot the ISO, my custom config as mentioned above is perfectly as it should be.

But if I boot it via PXE, TFTP and NFS, suddenly the hostname is changed to systemback and /usr/sbin/lightdm --show-config shows a completely different autologon. Why does this happen only in the case with PXE? How can I disable systemback to do these changes?

Thank You!