When conflict with images, can not reslove with TortoiseGitIDiff by Click select

1. Double click the conflicted image or right click and click Edit conflicts to open TortoiseGitIDiff
2. Choose one image and click select
   
   Expect: Resloved with the selected image
   Actually: TortoiseGitIDiff closed but nothing changed, Only got an temp file like .merge_file_a01172
   (Only right click the file in commit dialog, and click Resolve conflict using '*' works)

---

TortoiseGit 1.8.15.1 (D:\Tools\TortoiseGit\bin)
git version 2.5.2.windows.2 (20150820-da295330; D:\Tools\Git\bin; D:\Tools\Git\mingw64; D:\Tools\Git\mingw64\etc\gitconfig)