Calculate daily cumulative values appears to not be aligning water years correctly

import dataretrieval
import hyswap
df, _ = dataretrieval.nwis.get_dv(site='06892350',
parameterCd='00060',
start='1900-01-01',
end='2021-12-31')
cdf = hyswap.cumulative.calculate_daily_cumulative_values(
df, '00060_Mean', year_type = 'water')
cdf.head()

Notice that cdf shows '1918-10-01' as belonging to the 1918 water year, when it should belong to the 1919 water year.