Git 2.9 handles renaming of files differently to versions before
Git 2.9 Release Notes
=====================
Backward compatibility notes
----------------------------
The end-user facing Porcelain level commands in the "git diff" and
"git log" family by default enable the rename detection; you can still
use "diff.renames" configuration variable to disable this.
@mbabker apparently got there first in #11373 :P