Created attachment 4618
I'm not really sure whether it's a dbus bug or not, but in some conditions, the dbus spawn of xfconf leads to the shutdown of xfsettingsd because it "thinks" another instance is taking over... After some debugging I found that it receives a NameOwnerChanged signal describing the launch of Xfconf (name=org.xfce.Xfconf, old=, new=:1.11 for example).
The attached patch checks that the received message is valid and that it's actually intended for org.xfce.SettingsDaemon. It fixes this issue here.
Pushed in c17fe35.