Comment # 6 on bug 1131074 from Stefan Dirsch

Looks like you've removed /usr/share/xsessions/tde.desktop meanwhile.

Whatever. Highest number wins here. update-alternatives is in auto mode by
default, means highest number wins. You should switch to manual mode.

As documentation I'm aware of "update-alternatives --help" and the manual
page.

---
When using the --config option, update-alternatives will list all of the
choices for the link group of which given name is the master alternative name. 
The current choice is marked  with a  ���*���.   You  will then be prompted for
your choice regarding this link group.  Depending on the choice made, the link
group might no longer be in auto mode. You will  need  to  use  the --auto 
option in order to return to the automatic mode (or you can rerun --config and
select
the entry marked as automatic).
--

This is what you want for surviving the next "zypper up".