CategoricalIndex reidex duplicates values
From [SO question](https://stackoverflow.com/q/51228928/2901002):

**Sample**:

    np.random.seed(57)

    idx = pd.CategoricalIndex(['low'] * 3 + ['hi'] * 3)
    dfb = pd.DataFrame(np.random.rand(6, 3), columns=list('abc'), index=idx)
    print (dfb)
                a         b         c
    low  0.087350  0.230477  0.411061
    low  0.310783  0.565956  0.545064
    low  0.807099  0.918155  0.522091
    hi   0.424687  0.071804  0.898529
    hi   0.420514  0.582170  0.214154
    hi   0.447486  0.467864  0.100637

Round incorrectly explode rows:
    
    print (dfb.round(3))
             a      b      c
    low  0.087  0.230  0.411
    low  0.311  0.566  0.545
    low  0.807  0.918  0.522
    low  0.087  0.230  0.411
    low  0.311  0.566  0.545
    low  0.807  0.918  0.522
    low  0.087  0.230  0.411
    low  0.311  0.566  0.545
    low  0.807  0.918  0.522
    hi   0.425  0.072  0.899
    hi   0.421  0.582  0.214
    hi   0.447  0.468  0.101
    hi   0.425  0.072  0.899
    hi   0.421  0.582  0.214
    hi   0.447  0.468  0.101
    hi   0.425  0.072  0.899
    hi   0.421  0.582  0.214
    hi   0.447  0.468  0.101

Expected output:

    print (dfb.round(3))
             a      b      c
    low  0.087  0.230  0.411
    low  0.311  0.566  0.545
    low  0.807  0.918  0.522
    hi   0.425  0.072  0.899
    hi   0.421  0.582  0.214
    hi   0.447  0.468  0.101

---

    print (pd.show_versions())
    
    INSTALLED VERSIONS
    ------------------
    commit: None
    python: 3.6.4.final.0
    python-bits: 64
    OS: Windows
    OS-release: 7
    machine: AMD64
    processor: Intel64 Family 6 Model 42 Stepping 7, GenuineIntel
    byteorder: little
    LC_ALL: None
    LANG: en
    LOCALE: None.None
    
    pandas: 0.23.1
    pytest: 3.3.2
    pip: 9.0.1
    setuptools: 39.2.0
    Cython: 0.27.3
    numpy: 1.14.3
    scipy: 1.0.0
    pyarrow: None
    xarray: None
    IPython: 6.2.1
    sphinx: 1.6.6
    patsy: 0.5.0
    dateutil: 2.7.3
    pytz: 2018.4
    blosc: None
    bottleneck: 1.2.1
    tables: 3.4.2
    numexpr: 2.6.4
    feather: None
    matplotlib: 2.2.2
    openpyxl: 2.4.10
    xlrd: 1.1.0
    xlwt: 1.3.0
    xlsxwriter: 1.0.2
    lxml: 4.1.1
    bs4: 4.6.0
    html5lib: 1.0.1
    sqlalchemy: 1.2.1
    pymysql: None
    psycopg2: None
    jinja2: 2.10
    s3fs: None
    fastparquet: None
    pandas_gbq: None
    pandas_datareader: None
    None

    
