Thanks for the replies. Glad to hear it's not just me, although obviously I must be a bit too impatient. I have never left it long enough to find out if it disappears automatically if left long enough. That's fine if someone really is not wearing a seat belt, although I suspect there is also an audio warning in such situations, but if they are the diagram should disappear immediately IMHO (and as in most other cars). Hence my theory that it's a minor software bug.
IanG - Regarding the Lane Keeping Assist System, I have the opposite problem to you and want to turn it off completely, but it keeps coming back on every trip until I disable it (again). There must be a way in the settings to set it permanently on or off!