t7900 fails with recent debian systemd?

I noticed t7900 failing today. The failure looks like this:

  $ ./t7900-maintenance.sh -v -i -x
  [...]
  + systemd-analyze verify systemd/user/git-maintenance@hourly.service
  Unit git-maintenance@hourly.service not found.
  error: last command exited with $?=1
  not ok 36 - start and stop Linux/systemd maintenance

The problem started after upgrading my Debian unstable system to the systemd 255~rc4-2 deb. Downgrading back to 254.5-1 makes the test pass again.

I'm sure it's something silly with finding paths in XDG_CONFIG_HOME or something like that. I haven't dug further, but I thought I'd post this to save somebody else going through the same initial debugging. (And of course any wisdom or further debugging is greatly appreciated).

-Peff