GNU diff3 (three-way merge) gives unexpected result

Question

Assume that files MINE and YOURS are descendants of OLD.

FILE_MINE=

abc
def
ghi

FILE_OLD=

abc
jkl
ghi

FILE_YOURS=

abc
def
ghi

Command diff3 -m MIND OLD YOURS gives:

abc
<<<<<<< OLD
jkl
=======
def
>>>>>>> YOURS
ghi

diff3 cannot resolve that MINE and YOURS made identical changes.

Why? And, is there a way to resolve this issue?

Tickle your brain with this:

diff OLD MIND and diff OLD YOURS have identical hunks in their output.

2c2
< jkl
---
> def

Should these hunks not "cancel-out" during the three-way merge?