Series.sort_values using mergesort and descending is not stable

[has2k1]

Code Sample

import pandas as pd

s = pd.Series([1, 2, 1, 3], ['first', 'b', 'second', 'c'])
print(s.sort_values(ascending=False, kind='mergesort'))

Output

c         3
b         2
second    1
first     1
dtype: int64

Expected Output

c         3
b         2
first     1
second    1
dtype: int64

Problem description

Mergesort should be stable irrespective of direction, but ascending=False (which is not stable) is just the reverse of ascending=True (which is stable).

[mzeitlin11]

This looks to be fixed in master. Looks like there are tests for the dataframe case, but could use tests for the series case.

[na2shell]

take