stddev gives different results for 2 identical datasets in U-SQL

Question

I have 2 csv datasets with 1 column 'v'. The data in these 2 files are exactly same. The column 'v' contains values that would be converted to decimal? before performing stdev.

sum(v), avg(v) values are same in both the datasets, but stdev values are not matching. How is it even possible ?

Here is the code,

@ds1 =
EXTRACT v decimal?            
FROM @ds1_path
USING Extractors.Csv(skipFirstNRows : 1);

@ds2 = EXTRACT v decimal?            
FROM @ds2_path
USING Extractors.Csv(skipFirstNRows : 1);

@data =
SELECT STDEV(v) AS stdev,
       SUM(v) AS sum,
       AVG(v) AS avg,
       VAR(v) AS vari,
       "ds1" AS type
FROM @ds1
UNION ALL
SELECT STDEV(v) AS stdev,
       SUM(v) AS sum,
       AVG(v) AS avg,
       VAR(v) AS vari,
       "ds2" AS type
FROM @ds2;

This gives the following output. If you notice sum, avg values are exactly same, but VAR and STDEV values are not matching.

Can somebody please help ?

output