According to the description, `/users/{id}/tags/{tags}/top-answers` should return answers by the user on that particular tag.

> Returns the top 30 answers a user has posted in response to questions with the given tags.


However, what it appears to be doing is posting the top answers by any user on questions the user has asked in that tag.

[example URL][1]

    {
        "items": [{
            "question_id": 37051,
            "answer_id": 37238,
            "creation_date": 1321713089,
            "last_activity_date": 1321713089,
            "score": 31,
            "is_accepted": true,
            "owner": {
                "user_id": 12,
                "display_name": "Jeff Atwood",
                "reputation": 5238,
                "user_type": "moderator",
                "profile_image": "http://www.gravatar.com/avatar/51d623f33f8b83095db84ff35e15dbe8?d=identicon&r=PG",
                "link": "http://gaming.stackexchange.com/users/12/jeff-atwood",
                "accept_rate": 43
            }
        }, {
            "question_id": 33733,
            "answer_id": 33734,
            "creation_date": 1319994768,
            "last_activity_date": 1319994768,
            "score": 14,
            "is_accepted": true,
            "owner": {
                "user_id": 9752,
                "display_name": "lunboks",
                "reputation": 11504,
                "user_type": "registered",
                "profile_image": "http://www.gravatar.com/avatar/e73aa0432546c2c3c39dfcf1fa124c09?d=identicon&r=PG",
                "link": "http://gaming.stackexchange.com/users/9752/lunboks",
                "accept_rate": 90
            }
        }, {
            "question_id": 33733,
            "answer_id": 38377,
            "creation_date": 1322198871,
            "last_edit_date": 1322200473,
            "last_activity_date": 1322200473,
            "score": 0,
            "is_accepted": false,
            "owner": {
                "user_id": 15257,
                "display_name": "Black Knight",
                "reputation": 1,
                "user_type": "unregistered",
                "profile_image": "http://www.gravatar.com/avatar/895d9181500c9c2f28a279c89fd1ab78?d=identicon&r=PG",
                "link": "http://gaming.stackexchange.com/users/15257/black-knight"
            }
        }],
        "quota_remaining": 9892,
        "quota_max": 10000,
        "has_more": false
    }

[1]: http://api.stackexchange.com/2.0/users/821/tags/battlefield-3/top-answers?key=0p65aJUHxHo0G19*YF272A((&site=gaming