BUG: Inconsistent date resolution

[super-ibby]

Pandas version checks

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

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

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

Reproducible Example

import datetime
import pandas as pd
pd.__version__  # ‘2.2.2’

d = datetime.datetime(2025, 4, 10)

pd.Series([d]).dtype  # dtype('<M8[ns]')

pd.DataFrame([{'date': d}])['date'].dtype  # dtype('<M8[ns]')

df = pd.DataFrame([{'x': 0}])
df['date'] = d  # <— broadcast scalar
df['date'].dtype  # dtype('<M8[us]')  <— different date resolution!

Issue Description

Date resolution differs between Series/DataFrame construction versus assignment via a scalar broadcast.

Expected Behavior

I’d expect the same date resolution across the examples I provided.

Installed Versions

commit : d9cdd2e
python : 3.11.9.final.0
python-bits : 64
OS : Windows
OS-release : 10
Version : AMD64
processor : Intel64 Family 6 Model 85 Stepping 7, GenuineIntel
byteorder : little

pandas : 2.2.2
numpy : 1.26.4
Cython : 3.0.10

[asishm]

Thanks for the report. This seems to be fixed in main. Can you confirm you can reproduce this with the main branch (check box 3)?

[rhshadrach]

I'm seeing the same @asishm - closing.