translatable field properties "description" not used when in collection

likely not best title for this issue; but initially posted on the i18n module here: #1524922: field options are not translatable; but part of that issue is due to field_collection.

i think field_collection is doing a trick to show a field's description property (typically not shown except on edit form) when no values have been entered for that collection field: http://screencast.com/t/3S6akQeyz

it takes the parent fields #description property and adds it as a #prefix to the instance.

but it does not take the translated property.