Solved by mariosasko in post #2 
              
              
                Hi, 
this inconsistency is due to how PyArrow converts nested sequences to NumPy by default but can be fixed by casting the corresponding column to the ArrayXD type. 
E.g. in your example: 
dset = Dataset.from_dict(
    {"a": [[[2,1],[2,2]], [[3,1],[3,2]]], "b": [1,1]}, 
    features=Features({"a": …