[RFC] mailmap.blob overrides default .mailmap

Hi,

 I was reading into the mailmap handling today and I'm a bit puzzled by the overriding behavior.

This is what the documentation says about precedence (emphasis mine):
-------------
mailmap.file
    The location of an augmenting mailmap file. The default mailmap, located
    in the root of the repository, is loaded first, then the mailmap file
    pointed to by this variable. The location of the mailmap file may be in a
    repository subdirectory, or somewhere outside of the repository itself.
    See git-shortlog(1) and git-blame(1).

mailmap.blob
    Like mailmap.file, but consider the value as a reference to a blob in the
    repository. If both mailmap.file and mailmap.blob are given, both are
!!! parsed, with _entries from mailmap.file taking precedence_. In a bare
    repository, this defaults to HEAD:.mailmap. In a non-bare repository, it
    defaults to empty.
------------

So from the doc I would have expected that files always get precedence over the blob. IOW entries from .mailmap override entries from mailmap.blob. However, this is not the case.

The code shows why (mailmap.c):
	err |= read_mailmap_file(map, ".mailmap", repo_abbrev);
	if (startup_info->have_repository)
		err |= read_mailmap_blob(map, git_mailmap_blob, repo_abbrev);
	err |= read_mailmap_file(map, git_mailmap_file, repo_abbrev);

Apparently this is not an oversight, because there is an explicit test for this overriding behavior (t4203 'mailmap.blob overrides .mailmap').

So I wonder: what is the rationale behind this? I find this mixed overriding behavior hard to explain and difficult to understand.