[web2py] image in form

[peter]

I define a table


db.define_table('artists',
                Field('name'),
                Field('image','upload'),
                ..)

I edit it it as follows

@auth.requires_login()
def edit_artist():
    artist = db(db.artists.id==request.args(0)).select().first()
    form = SQLFORM(db.artists, artist)
    if form.accepts(request.vars, session):
        redirect(URL('artist', args=artist.name))
    elif form.errors:
        response.flash = form.errors.b

    return(dict(form=form))

However there is always a 'no file chosen message by the image in the
edit form. The image definitely is defined as it appears correctly
when the record is displayed.

I can update the image and the message goes away, but if I then try
and edit the record again, I again get the 'no file chosen' message.

Peter