Merge behavior with merge.conflictStyle diff3

Hi,

I´m not sure if this is a bug or not.

These are the steps to reproduce it (git 2.17 at least):
- In a repo, with default settings (merge strategy, conflict style,
merge drivers, etc);
- Create a file 'test.xml', and add the following content to it:

[div]
  A
[/div]

- Perform a git add and git commit, then, create a branch named branch1;
- Next, on branch1, edit the xml file and add a new div:

[div]
  A
[/div]
[div]
  B
[/div]

- Then, comit the changes, and after that return to branch master;
- So, perform a similar but slightly different change:

[div]
  A
[/div]
[div]
  C
[/div]

- Then commit it;
- Now, do a merge (git merge branch1);

When my conflictStyle is default (merge), the merged file becames:
[div]
[[[[[[[ HEAD
  C
=======
  B
]]]]]]] branch1
[/div]

But when the merge.conflictStyle is set to diff3, I get:
[[[[[[[ HEAD
[div]
  C
[/div]
||||||| merged common ancestors
=======
[div]
  B
[/div]
]]]]]]] branch1

I guess, most times the second behavior is the expected: two conflict hunks, not only the divvergent pieces (this case, the second line) of them. By the doc:

merge.conflictStyle

    Specify the style in which conflicted hunks are written out to
working tree files upon merge. The default is "merge", which shows a
[[[[[[[ conflict marker, changes made by one side, a ======= marker,
changes made by the other side, and then a ]]]]]]] marker. An
alternate style, "diff3", adds a ||||||| marker and the original text
before the ======= marker.

I replaced the 'lower than' and 'greater than' symbols by 'open n close square brackets' to avoid antivirus.

Is this a bug, or something I missunderstood from git docs?

Thanks, Adilson de Almeida Jr