+Behavior on bound-redisplay is a bit funky, because of hardcoded
+special-casing of FileField in Django's forms.py. FileField's are
+special-cased in BaseForm._clean_fields to receive initial (in
+addition to submitted) data in their clean() method, and also in
+BoundField.as_widget() to have initial data rendered as the value if
+no new data was submitted. Since we inherit from MultiValueField
+rather than FileField, we don't get this special-casing, and so our
+FileField always renders empty on bound redisplay when a regular
+FileField would render the initial data.
+Ideally Django would be fixed to remove this special-casing of
+FileField, either making it polymorphic behavior on fields/widgets or
+based on a Field class attribute flag, or some such. Then we could
+pretend to be a FileField and be able to emulate that behavior.