or is it reloaded anew every time the Preferences dialog is re-opened?
Yes, in function ```prefs_init_dialog()``` in file ```prefs.c``` the dialog is synced to the global value: ``` C gtk_toggle_button_set_active(GTK_TOGGLE_BUTTON(widget), project_prefs.use_project_session_files); ``` Also, the Workbench plugin is only temporarily setting the value to ```FALSE``` and then restores the old value.