Group audience field not rendered when more than one form present on the same page

Problem/Motivation

I have two group content types, post and image, that belong to a group.
In the group page, I show both the post and image forms with blocks.
Only the first form shows the group audience field.

Proposed resolution

I've tracked down the issue to the og.field.inc file, line #45

  $identifier = $field_name . ':' . $entity_type . ':' . $id;
  if (isset($cache[$identifier])) {
    return array();
  }

The identifier is something like og_group_ref:node: for create forms, but it's missing the bundle property so renders after the first one just skip the field.
Adding the bundle, available a few lines above (#42), solves the problem.

  $identifier = $field_name . ':' . $entity_type . ':' . $bundle . ':' . $id;