Comparing with added file might result in comparison with empty file

What steps will reproduce the problem?

1. add a empty text file and commit.
2. modify the text file and commit.
3. execute "Git Show Log"
4. make the lastest text file for comparison.
5. diff the previous empty text file with the lastest text file.

What is the expected output? What do you see instead?

i expected show comparison result of empty content vs. modified content, but it's not.

see the animation:

Repository: mygit.7z

What version of TortoiseGit and Git are you using? On what operating system?

TortoisesGit version is 2.1.0.0 on Windows 10

Please provide any additional information below.

it's a bug ???