I have tested the new proposed workaround listed in comment #13 using the 2013.2 release (in devstack).  The workaround is behaving correctly for me:

[nkinder@localhost devstack]$ source openrc admin admin
[nkinder@localhost devstack]$ glance image-create --property provider_foo=foo --name foo
+-------------------------+--------------------------------------+
| Property                | Value                                |
+-------------------------+--------------------------------------+
| Property 'provider_foo' | foo                                  |
| checksum                | None                                 |
| container_format        | None                                 |
| created_at              | 2014-05-31T00:04:44                  |
| deleted                 | False                                |
| deleted_at              | None                                 |
| disk_format             | None                                 |
| id                      | a8fbd50a-5871-433d-9097-5d3320339d98 |
| is_public               | False                                |
| min_disk                | 0                                    |
| min_ram                 | 0                                    |
| name                    | foo                                  |
| owner                   | 6cad2594f37549798970593027b587b3     |
| protected               | False                                |
| size                    | 0                                    |
| status                  | queued                               |
| updated_at              | 2014-05-31T00:04:44                  |
| virtual_size            | None                                 |
+-------------------------+--------------------------------------+


[nkinder@localhost devstack]$ source openrc demo demo
[nkinder@localhost devstack]$ glance image-create --property provider_bar=bar --name bar
403 Forbidden
Property 'provider_bar' is protected
    (HTTP 403)
[nkinder@localhost devstack]$ glance image-create --property junk_bar=bar --name bar
+---------------------+--------------------------------------+
| Property            | Value                                |
+---------------------+--------------------------------------+
| Property 'junk_bar' | bar                                  |
| checksum            | None                                 |
| container_format    | None                                 |
| created_at          | 2014-05-31T00:05:46                  |
| deleted             | False                                |
| deleted_at          | None                                 |
| disk_format         | None                                 |
| id                  | 4ce3b1de-d5ad-46ac-acbe-2d0ed50d53c8 |
| is_public           | False                                |
| min_disk            | 0                                    |
| min_ram             | 0                                    |
| name                | bar                                  |
| owner               | 6cad2594f37549798970593027b587b3     |
| protected           | False                                |
| size                | 0                                    |
| status              | queued                               |
| updated_at          | 2014-05-31T00:05:46                  |
| virtual_size        | None                                 |
+---------------------+--------------------------------------+