"npmat @ pdseries" should be equivalent to "npmat @ pdseries.values"

[philip4096]

Code Sample

import pandas as pd
import numpy as np

npmat = np.array([[1, 0],[1, 1]])
pdseries = pd.Series([1, 2])

np.testing.assert_allclose(npmat @ pdseries, npmat @ pdseries.values ) # fails but should succeed

Problem description

Maybe there is a good explanation but I did not expect this.
It is unexpected that npmat @ pdseries is NOT equivalent to npmat @ pdseries.values.
It is unexpected that npmat @ pdseries, is equvivalent to pdseries.values @ npmat.

Expected Output

nothing

Output of pd.show_versions()

[paste the output of pd.show_versions() here below this line]
INSTALLED VERSIONS

commit: None
python: 3.6.3.final.0
python-bits: 64
OS: Windows
OS-release: 10
machine: AMD64
processor: Intel64 Family 6 Model 158 Stepping 9, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None
pandas: 0.23.4
pytest: 3.7.1
pip: 18.1
setuptools: 36.5.0.post20170921
Cython: 0.26.1
numpy: 1.14.5
scipy: 1.1.0
pyarrow: None
xarray: None
IPython: 6.1.0
sphinx: 1.6.3
patsy: 0.4.1
dateutil: 2.6.1
pytz: 2017.2
blosc: None
bottleneck: 1.2.1
tables: 3.4.2
numexpr: 2.6.2
feather: None
matplotlib: 2.1.0
openpyxl: 2.4.8
xlrd: 1.1.0
xlwt: 1.3.0
xlsxwriter: 1.0.2
lxml: 4.1.0
bs4: 4.6.0
html5lib: 0.999999999
sqlalchemy: 1.1.13
pymysql: None
psycopg2: None
jinja2: 2.9.6
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None

[TomAugspurger]

Your assert passes for me locally.

There was a bug in rmatmul, but that was fixed in #21530. Can you double check your pandas version?

[philip4096]

My pandas version is pandas: 0.23.4 according to pd.show_versions() and conda. I reinstalled it. Should it work in this version?

[TomAugspurger]

I just tried with 0.23.4 and it's indeed broken. But it works on master so it must have been fixed in the interim.

If you're interested, you can try pulling down master to see if things work. Let me know if not and we'll reopen.