I have the same issue, but I don't have the systemd error message. I'm using xdm to log in and starting sawfish from the .xsession file.
As well as using my usual configuration that has worked for several years, I can reproduce it simply like this: 1) create a new user 2) log in to the console with new user 3) echo sawfish > .xsession 4) log in to xdm with the new user result: 1) user is logged in 2) session immediately exits 3) xdm login screen is shown again I'm using the testing distribution. The issue showed up after the last update. The issue does not exist with other window managers (tried xfce, fluxbox, enlightenment).
