Contact Reference fields do not work in profiles present on "On Behalf Of" Contribution pages.

Steps to reproduce:

1. Create a custom field set for an organization.
2. Add a Contact Reference field to the set.
3. Create a new Contribution page.
4. Check "Allow individuals to contribute and / or signup for membership on behalf of an organization?"
5. Select "On Behalf Of Organization" as the profile and edit it.
6. Add the previously created custom field.

If you hit preview on the edit page, you see the expected bahavior of the field. However, if you save the page and visit either the test link or the production links, the field appears as a text field.

Discussion: https://civicrm.stackexchange.com/questions/3444/how-to-use-auto-complete-reference-field-in-a-profile/
Example: http://d46.demo.civicrm.org/civicrm/contribute/transact?reset=1&action=preview&id=4

In this case, the "Rep" field should be a Contact Reference field. The field works fine when embeded other places.