Comment # 15 on bug 968405 from Egbert Eich

(In reply to Dr. Werner Fink from comment #11)
> (In reply to Dominique Leuenberger from comment #9)
> 
> Then explain how we solve both this bug and bsc#955996
> 
> If one use DISABLE_STOP_ON_REMOVAL != yes the nhe gets what has been
> requested.
> 
> I'll not change back to solve this bug and open the other here.

I don't think we can. No matter what, if %preun and %postun are run both during
update and removal, we just cannot take down the display manager.
In fact, I'd argue that even during removal it would be unfriendly to kill a
running session when the xdm package is removed. So the only time when you can
safely terminate it is when no user is logged in.
Once the display-manager is terminated it won't restart if xdm is gone, but as
long as it is running it will stay running. Even when the user logs out, a DM
isn't restarted, thus even though xdm has been removed or updated, the old
state remains running.