Difference between i;;j and {i,...,j} output as dataset descending operators

I'm trying to understand the difference between {part1, part2, ...} and part1 ;; part2 descending operators semantics for datasets, and I uncovered that they behave differently from what I expect.
Let's create some sample dataset:
In[]:=
data=Dataset[Association[Thread[{"a","b","c"}#]]&/@Partition[Range[12],3]]
Out[]=
a
b
c
1
2
3
4
5
6
7
8
9
10
11
12
What looks like a bug is that the following two expressions provide a differently formatted output,
In[]:=
data[All,2;;3]
Out[]=
b
2
c
3
b
5
c
6
b
8
c
9
b
11
c
12
In[]:=
data[[All,2;;3]]
Out[]=
b
2
c
3
b
5
c
6
b
8
c
9
b
11
c
12
In[]:=
data[All,{2,3}]
Out[]=
b
c
2
3
5
6
8
9
11
12
In[]:=
data[[All,{2,3}]]
Out[]=
b
c
2
3
5
6
8
9
11
12
even though their normal forms are exactly the same, and "intuitively", they should mean the same thing?
In[]:=
Normal[data[All,{2,3}]]==Normal[data[All,2;;3]]
Out[]=
True
The documentation for Dataset has the following explanations in the Details section, which doesn't clarify things much:
◼
  • dataset[[All,m;;n]] extract columns m through n
    • ◼
  • dataset[[All,{n1,n2,…}]] extract a subset of the columns
    • and in Descending operators subsection
    ◼
  • i;;j take parts i through j and apply subsequent operators to each part
    • ◼
  • {part1,part2,…} take given parts and apply subsequent operators to each part
    • Note that if we apply these two different forms of Part to the underlying association, they yield the same results.
    In[]:=
    data1=Association[Thread[{"a","b","c"}#]]&/@Partition[Range[12],3]
    Out[]=
    {a1,b2,c3,a4,b5,c6,a7,b8,c9,a10,b11,c12}
    In[]:=
    data1[[All,{2,3}]]
    Out[]=
    {b2,c3,b5,c6,b8,c9,b11,c12}
    In[]:=
    data1[[All,2;;3]]
    Out[]=
    {b2,c3,b5,c6,b8,c9,b11,c12}
    Could someone knowledgeable please confirm whether this indicates a gap in my understanding, or a bug in Dataset output form?