Multiple aggregations with the same name get overwritten

[MarcoGorelli]

Code Sample, a copy-pastable example if possible

import pandas as pd
import numpy as np
from functools import partial

df = pd.DataFrame(
    np.random.randn(1000, 3), 
    index=pd.date_range('1/1/2012', freq='S', periods=1000), 
    columns=['A', 'B', 'C']
)
dfg = df.resample('3T').agg(
    {'A': [
        partial(np.quantile, q=.9999), 
        partial(np.quantile, q=.1111),
    ]}
)

returns

                            A          
                     quantile  quantile
2012-01-01 00:00:00 -1.035997 -1.035997
2012-01-01 00:03:00 -1.326052 -1.326052
2012-01-01 00:06:00 -1.267661 -1.267661
2012-01-01 00:09:00 -1.321961 -1.321961
2012-01-01 00:12:00 -1.103027 -1.103027
2012-01-01 00:15:00 -0.987614 -0.987614

Output of pd.show_versions()

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

commit : 5e9fe4e
python : 3.7.3.final.0
python-bits : 64
OS : Linux
OS-release : 4.15.0-74-generic
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_GB.UTF-8
LOCALE : en_GB.UTF-8

pandas : 0.25.0+1719.g5e9fe4e08.dirty
numpy : 1.17.3
pytz : 2019.3
dateutil : 2.8.0
pip : 19.3.1
setuptools : 42.0.2.post20191201
Cython : 0.29.14
pytest : 5.3.2
hypothesis : 4.55.4
sphinx : 2.3.0
blosc : None
feather : None
xlsxwriter : 1.2.6
lxml.etree : 4.4.2
html5lib : 1.0.1
pymysql : None
psycopg2 : None
jinja2 : 2.10.3
IPython : 7.9.0
pandas_datareader: None
bs4 : 4.8.1
bottleneck : 1.3.1
fastparquet : 0.3.2
gcsfs : None
lxml.etree : 4.4.2
matplotlib : 3.1.2
numexpr : 2.7.0
odfpy : None
openpyxl : 3.0.1
pandas_gbq : None
pyarrow : 0.15.1
pytables : None
pytest : 5.3.2
s3fs : 0.4.0
scipy : 1.4.0
sqlalchemy : 1.3.11
tables : 3.6.1
tabulate : 0.8.6
xarray : 0.14.1
xlrd : 1.2.0
xlwt : 1.3.0
xlsxwriter : 1.2.6
numba : 0.46.0