Comment # 16 on bug 934901 from Egbert Eich

I see three options to resolve this:

1. Not restart systemd-logind on post-inst as suggested
2. Implement the solution to pass fds from an old systemd-logind to the new one 
   to help lazy Mr Poettering over the hump.
3. Change the handling in the Xserver to not rudely kill the server but fail 
   subsequent VT switches if systemd-logind has been restarted logging an
   informative message stating the reason.

A potential downside of 3 may be that suspend will stop working. This would
have to be investigated. If this really was the case I would not consider 3 a
valid option: while I could live with not being able to VT switch my Xserver I
would really dislike to no longer be able to suspend my laptop just because
there happened to be an update to systemd.

In any case I won't be able to look into this for the next 2-3 weeks.