Bug#762041: systemd: upgrading systemd results in /run/user/<uid> being emptied

[Uoti Urpala]

I checked that this did not happen on a system I just updated from 204
to 215; contents of /run/user/1000 remained unchanged after the upgrade.

Are you sure that the upgrade actually *removed* contents? A possibly
relevant change is that logind started to mount a per-user tmpfs
in /run/user/* (for per-user size limits). If something on your system
triggered a mount of a new tmpfs over the existing directory, that could
give similar symptoms.