BUG: Incorrect result when method!=None for MultiIndex.get_indexer

[galipremsagar]

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• I have confirmed this bug exists on the main branch of pandas.

Reproducible Example

In [1]: import pandas as pd

In [2]: idx = pd.MultiIndex.from_tuples(
   ...:             [(2, 1, 1), (1, 2, 3), (1, 2, 1), (1, 1, 10), (1, 1, 1), (2, 2, 1)]
   ...:         )

In [3]: idx.get_indexer(((1, 2, 3),))
Out[3]: array([1])

In [4]: idx.get_indexer(((1, 2, 3),), method='bfill')
Out[4]: array([0])

In [5]: idx.get_indexer(((1, 2, 3),), method='ffill')
Out[5]: array([-1])

Issue Description

According to the docstring method should actually kick only when the element is not found(i.e., -1) in the result. So I expect results for this specific set of inputs to be [1] always.

Expected Behavior

In [4]: idx.get_indexer(((1, 2, 3),), method='bfill')
Out[4]: array([1])

In [5]: idx.get_indexer(((1, 2, 3),), method='ffill')
Out[5]: array([1])

Installed Versions

INSTALLED VERSIONS

commit : 965ceca
python : 3.10.11.final.0
python-bits : 64
OS : Linux
OS-release : 4.15.0-76-generic
Version : #86-Ubuntu SMP Fri Jan 17 17:24:28 UTC 2020
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 2.0.2
numpy : 1.23.5
pytz : 2023.3
dateutil : 2.8.2
setuptools : 67.7.2
pip : 23.1.2
Cython : 0.29.34
pytest : 7.3.1
hypothesis : 6.75.3
sphinx : 5.3.0
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.1.2
IPython : 8.13.2
pandas_datareader: None
bs4 : 4.12.2
bottleneck : None
brotli :
fastparquet : None
fsspec : 2023.5.0
gcsfs : None
matplotlib : None
numba : 0.56.4
numexpr : None
odfpy : None
openpyxl : 3.1.2
pandas_gbq : None
pyarrow : 11.0.0
pyreadstat : None
pyxlsb : None
s3fs : 2023.5.0
scipy : 1.10.1
snappy :
sqlalchemy : 2.0.15
tables : None
tabulate : 0.9.0
xarray : None
xlrd : None
zstandard : None
tzdata : 2023.3
qtpy : None
pyqt5 : None

[galipremsagar]

cc: @mroeschke

[taytzehao]

take

[lukemanley]

Thanks for the report. The example in the OP is using a non-monotonic index which should actually raise when method is not None. I've opened #55352 to raise in this case.