I'd vote for the session settings dialog to not register with the session manager, if it does so at all. Here's my entry from .cache/sessions/: Legacy1_Screen=0 Legacy1_Command=xfce4-session-settings Legacy1_ClientMachine=alucardo I prefer to save my session using the settings dialog because I only want to save it once - the logout dialog is not well suited for that (with which I'm fine btw).
All gtk apps "register" with the session manager in the old X11R5 way. It's annoying... I think they implemented that around gtk 2.14 or so. You can fake it out, just hadn't gotten around to it. Really, we should do this for all the settings dialogs, I think. Is there any reason why anyone would want settings dialogs saved in their session?
I vote for removing it for all settings dialogs. I've googled a bit, but couldn't find the offending change in gtk. I totally agree, this is very annoying. I don't think this is appropriate default behavior.
*** This bug has been marked as a duplicate of bug 5113 ***