Happens to me on occasions too. Also when I restart I get a little black square appear because Homescreen Dockbar has taken it upon itself to create a new dockbar. When I get rid of this extra bit my dockbars disappear also. At the moment it seems to be behaving itself. If I remember correctly there was always a problem with Python widgets that caused all widgets to disappear from the homescreens. Not sure if this is it rearing it's ugly head again. Can't even remember if it got fixed in a Nokia update.