session management and save_type in save yourself message

Hi,

I've been reading some old threads such as https://listman.redhat.com/pipermail/xdg-list/2002-July/000615.html but I still don't understand why I receive some save yourself message with a save_style being 0xFF.
When I connect to the session manager using the SESSION_MANAGER env variable, I got a first save yourself message, to which I answer with a save yourself done, to which the SM answers with a save complete. message followed by a new save yourself message, but with 0xFF as save type. 
Does anyone know what that save_type is supposed to mean ? And what is expected as an answer ?

Note that all those extra messages disappear when I use the value of DESKTOP_AUTOSTART_ID env variable during my connection.

I have the feeling this is not the proper mailing list, so do not hesitate to re-route me to a more appropriated list.

Regards,
Iban.