Fix unintended autosaving of preferences in a few cases

* Dirty flag was not cleared on load
* Navigating tabs should not cause save
* Background mode should not autosave (for e.g. render farms and tests)

source/blender/blenloader/intern/readfile.c

@@ -9609,6 +9609,9 @@ static BHead *read_userdef(BlendFileData *bfd, FileData *fd, BHead *bhead)
   /* Don't read the active app template, use the default one. */
   user->app_template[0] = '\0';
 
+  /* Clear runtime data. */
+  user->runtime.is_dirty = false;
+
   /* free fd->datamap again */
   oldnewmap_free_unused(fd->datamap);
   oldnewmap_clear(fd->datamap);

source/blender/editors/interface/interface_handlers.c

@@ -7575,8 +7575,9 @@ static void button_activate_exit(
     }
 
     /* Not very elegant, but ensures preference changes force re-save. */
-    if (but->rnaprop && (but->rnapoin.data == &U)) {
+    if (but->rnaprop && (but->rnapoin.data == &U) && !RNA_property_update_check(but->rnaprop)) {
       U.runtime.is_dirty = true;
+      WM_main_add_notifier(NC_WINDOW, NULL);
     }
   }
 

source/blender/makesrna/intern/rna_userdef.c

@@ -184,6 +184,13 @@ static void rna_userdef_version_get(PointerRNA *ptr, int *value)
   value[2] = userdef->subversionfile;
 }
 
+static void rna_userdef_ui_update(Main *UNUSED(bmain),
+                                  Scene *UNUSED(scene),
+                                  PointerRNA *UNUSED(ptr))
+{
+  WM_main_add_notifier(NC_WINDOW, NULL);
+}
+
 static void rna_userdef_update(Main *UNUSED(bmain), Scene *UNUSED(scene), PointerRNA *UNUSED(ptr))
 {
   /* We can't use 'ptr->data' because this update function
@@ -5591,7 +5598,7 @@ void RNA_def_userdef(BlenderRNA *brna)
   RNA_def_property_enum_items(prop, preference_section_items);
   RNA_def_property_ui_text(
       prop, "Active Section", "Active section of the preferences shown in the user interface");
-  RNA_def_property_update(prop, 0, "rna_userdef_update");
+  RNA_def_property_update(prop, 0, "rna_userdef_ui_update");
 
   /* don't expose this directly via the UI, modify via an operator */
   prop = RNA_def_property(srna, "app_template", PROP_STRING, PROP_NONE);

source/blender/windowmanager/intern/wm_init_exit.c

@@ -475,7 +475,7 @@ void WM_exit_ext(bContext *C, const bool do_python)
       ED_screen_exit(C, win, WM_window_get_active_screen(win));
     }
 
-    if (U.runtime.is_dirty) {
+    if (U.runtime.is_dirty && !G.background) {
       if (U.pref_flag & USER_PREF_FLAG_SAVE) {
         BKE_blendfile_userdef_write_all(NULL);
       }