BUG: df reassignment following reorder_categories changed behavior in 1.1.0rc0

[MaozGelbart]

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• (optional) I have confirmed this bug exists on the master branch of pandas.

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Code Sample, a copy-pastable example

import pandas as pd

h = pd.Series(list("mn")).astype("category")
df = pd.DataFrame({"h":h})

df.h = df.h.cat.reorder_categories(["n", "m"])
print(df.h.cat.categories)

h = h.cat.reorder_categories(["n","m"])
print(h.cat.categories)

Problem description

Output with 1.1.0rc0:

Index(['m', 'n'], dtype='object')
Index(['n', 'm'], dtype='object')

The assignment of the reordered series back into the dataframe seems to remove the new order. This has changed from 1.0.5 but I could not find a note on this under the release notes.

Expected Output

As with 1.0.5:

Index(['n', 'm'], dtype='object')
Index(['n', 'm'], dtype='object')

Output of pd.show_versions()

INSTALLED VERSIONS

commit : bfac136
python : 3.8.3.final.0
python-bits : 64
OS : Darwin
OS-release : 19.5.0
Version : Darwin Kernel Version 19.5.0: Tue May 26 20:41:44 PDT 2020; root:xnu-6153.121.2~2/RELEASE_X86_64
machine : x86_64
processor : i386
byteorder : little
LC_ALL : None
LANG : None
LOCALE : None.UTF-8

pandas : 1.1.0rc0
numpy : 1.19.0
pytz : 2020.1
dateutil : 2.8.1
pip : 20.1.1
setuptools : 49.2.0.post20200712
Cython : None
pytest : 5.4.3
hypothesis : None
sphinx : 2.3.1
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 2.11.2
IPython : 7.15.0
pandas_datareader: None
bs4 : None
bottleneck : None
fsspec : None
fastparquet : None
gcsfs : None
matplotlib : 3.3.0
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : None
pytables : None
pyxlsb : None
s3fs : None
scipy : 1.4.1
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
numba : None

[simonjayhawkins]

Thanks @MaozGelbart for the report.

it appears #32831 resulted in this change of behaviour.

d427335 is the first bad commit
commit d427335
Author: jbrockmendel [email protected]
Date: Sat Mar 21 14:00:30 2020 -0700

BUG: ExtensionBlock.set not setting values inplace (#32831)

marking as regression for now, while further investigate.

cc @jbrockmendel

[TomAugspurger]

Closing as a duplicate of #33457