MySQL全文搜索布尔模式无法匹配'christoffer82'问题求助

使用MySQL布尔模式全文搜索时，无法匹配包含词根'christo'的'christoffer82'这类登录名，但匹配'johan84'的查询能正常返回结果。已知'christoffer82'在BDT_USERS_DUMMY表中仅出现1次（未超过结果集的50%），且不属于系统排除词，尝试过各类解决方案后问题仍未解决。

异常查询（无返回结果） #

SELECT
    usr.ID_USER AS userId
    , usr.USER_LOGIN AS userLogin
    , usr.EMAIL AS email
    , usr.MOBILE_PHONE AS mobilePhone
    , usr.FIRSTNAME AS firstName
    , usr.SURNAME AS surname
    , usr.USER_CREATED AS userCreated
    , usr.DATE_CREATED AS dateCreated
    , usr.USER_MODIFIED AS userModified
    , usr.DATE_MODIFIED AS dateModified
FROM
    BDT_USERS_DUMMY usr
WHERE 
    MATCH (usr.USER_LOGIN) AGAINST ('+christoffer82' IN BOOLEAN MODE)

正常查询（可返回对应结果） #

SELECT
    usr.ID_USER AS userId
    , usr.USER_LOGIN AS userLogin
    , usr.EMAIL AS email
    , usr.MOBILE_PHONE AS mobilePhone
    , usr.FIRSTNAME AS firstName
    , usr.SURNAME AS surname
    , usr.USER_CREATED AS userCreated
    , usr.DATE_CREATED AS dateCreated
    , usr.USER_MODIFIED AS userModified
    , usr.DATE_MODIFIED AS dateModified
FROM
    BDT_USERS_DUMMY usr
WHERE 
    MATCH (usr.USER_LOGIN) AGAINST ('+johan84' IN BOOLEAN MODE)

内容的提问来源于stack exchange，提问作者Loxio