/revisions/{ids} returns results where revision_number is always 1

Question

As of now, Code Review Question 59285 has three revisions, excluding the original question.

If I fetch those three revisions using the API, I see that all of them have revision_number set to 1.

That's a bug, right?

{
  "items": [
    {
      "user": {
        "reputation": 36810,
        "user_id": 9357,
        "user_type": "moderator",
        "profile_image": "https://i.sstatic.net/1f9W9.png?s=128&g=1",
        "display_name": "200_success",
        "link": "https://codereview.stackexchange.com/users/9357/200-success"
      },
      "tags": [
        "c++",
        "optimization",
        "c++11",
        "datetime"
      ],
      "set_community_wiki": false,
      "is_rollback": false,
      "creation_date": 1407360639,
      "post_id": 59285,
      "post_type": "question",
      "revision_type": "single_user",
      "revision_number": 1,
      "comment": "edited tags",
      "revision_guid": "886CBD37-096D-4309-A62E-902D823A38D8"
    },
    {
      "user": {
        "reputation": 486,
        "user_id": 13898,
        "user_type": "registered",
        "profile_image": "https://www.gravatar.com/avatar/529c8f8b57005502e37041f2eea75883?s=128&d=identicon&r=PG&f=1",
        "display_name": "Webby",
        "link": "https://codereview.stackexchange.com/users/13898/webby"
      },
      "set_community_wiki": false,
      "is_rollback": false,
      "creation_date": 1407357372,
      "post_id": 59285,
      "post_type": "question",
      "revision_type": "single_user",
      "revision_number": 1,
      "comment": "added 228 characters in body",
      "revision_guid": "CCCEA1F9-A1A2-4FE0-B598-726149DAADA0"
    },
    {
      "user": {
        "reputation": 16173,
        "user_id": 22222,
        "user_type": "moderator",
        "profile_image": "https://i.sstatic.net/a4zmY.jpg?s=128&g=1",
        "display_name": "Jamal",
        "link": "https://codereview.stackexchange.com/users/22222/jamal"
      },
      "tags": [
        "c++",
        "optimization",
        "c++11"
      ],
      "set_community_wiki": false,
      "is_rollback": false,
      "creation_date": 1407352574,
      "post_id": 59285,
      "post_type": "question",
      "revision_type": "single_user",
      "revision_number": 1,
      "title": "Checking whether a given timestamp is more than two weeks old",
      "comment": "added 4 characters in body; edited tags; edited title",
      "revision_guid": "9547C3CC-D473-431C-A96A-3274148935E3"
    }
  ],
  "has_more": false,
  "quota_max": 10000,
  "quota_remaining": 9909
}