Is there a bug in package Market Data?

Maybe the package MarketData has a small bug. I ran the following:

using Dates, DataFrames, MarketData
DataFrame(yahoo("^GSPC"))

The result is a dataframe with the last line duplicated. This is what is printed on the screen after running the code above:

12887×7 DataFrame
   Row │ timestamp   Open     High     Low      Close    AdjClose  Volume   ⋯
       │ Date        Float64  Float64  Float64  Float64  Float64   Float64  ⋯
───────┼─────────────────────────────────────────────────────────────────────
     1 │ 1971-02-08     0.0     98.04    96.13    97.45     97.45  2.559e7  ⋯
     2 │ 1971-02-09     0.0     98.5     96.9     97.51     97.51  2.825e7   
     3 │ 1971-02-10     0.0     97.97    96.23    97.39     97.39  1.904e7   
     4 │ 1971-02-11     0.0     98.49    96.99    97.91     97.91  1.926e7   
     5 │ 1971-02-12     0.0     98.96    97.56    98.43     98.43  1.847e7  ⋯
     6 │ 1971-02-16     0.0     99.59    97.85    98.66     98.66  2.135e7   
     7 │ 1971-02-17     0.0     99.32    97.32    98.2      98.2   1.872e7   
     8 │ 1971-02-18     0.0     98.6     96.96    97.56     97.56  1.665e7   
   ⋮   │     ⋮          ⋮        ⋮        ⋮        ⋮        ⋮          ⋮    ⋱
 12880 │ 2022-03-02  4322.56  4401.48  4322.56  4386.54   4386.54  4.40909e ⋯
 12881 │ 2022-03-03  4401.31  4416.78  4345.56  4363.49   4363.49  4.06208e  
 12882 │ 2022-03-04  4342.12  4342.12  4284.98  4328.87   4328.87  4.55825e  
 12883 │ 2022-03-07  4327.01  4327.01  4199.85  4201.09   4201.09  5.50633e  
 12884 │ 2022-03-08  4202.66  4276.94  4157.87  4170.7    4170.7   6.237e9  ⋯
 12885 │ 2022-03-09  4223.1   4299.4   4223.1   4277.88   4277.88  4.22018e  
 12886 │ 2022-03-10  4252.55  4268.28  4209.8   4259.52   4259.52  4.00869e  
 12887 │ 2022-03-10  4252.55  4268.28  4209.8   4259.52   4259.52  2.58114e  
                                              1 column and 12871 rows omitted

The last line, for March 10, 2022, is duplicated. Am I missing something or is this a bug?

Thanks.

Not a bug, but not certain what it is. You see it is also displayed on the website: S&P 500 (^GSPC) Historical Data - Yahoo Finance

Perhaps they are reporting after-market volume this way?

EDIT: Market is now open and that line is gone, so perhaps it was something related to overnight volume (volume was the only field that was different). Or maybe it is a bug – just at Yahoo

Yes. If one is not interested in the Volume column then after removing it the problem can be fixed using unique.

DataFrame(yahoo("^GSPC"))[:, [:timestamp, :AdjClose]] |>
unique
12886×2 DataFrame
   Row │ timestamp   AdjClose 
       │ Date        Float64
───────┼──────────────────────
     1 │ 1971-02-08     97.45
     2 │ 1971-02-09     97.51
     3 │ 1971-02-10     97.39
     4 │ 1971-02-11     97.91
     5 │ 1971-02-12     98.43
     6 │ 1971-02-16     98.66
     7 │ 1971-02-17     98.2
     8 │ 1971-02-18     97.56
   ⋮   │     ⋮          ⋮
 12879 │ 2022-03-01   4306.26
 12880 │ 2022-03-02   4386.54
 12881 │ 2022-03-03   4363.49
 12882 │ 2022-03-04   4328.87
 12883 │ 2022-03-07   4201.09
 12884 │ 2022-03-08   4170.7
 12885 │ 2022-03-09   4277.88
 12886 │ 2022-03-10   4259.52
            12870 rows omitted

If one is interested in the volume then a better understanding of the data is needed before taking action.