Git and KDiff3 on the Ubuntu subsystem

I use KDiff3 (executable kdiff3.exe) in Git Bash as git difftool and I encountered a problem to use it under the Ubuntu subsystem.

The Ubuntu subsystem has already Git installed. So I copied my Git global configuration from Git Bash (changing the path accordingly):

[user]    email = ...    name = ...[merge]    tool = kdiff3[mergetool "kdiff3"]    path = "/mnt/c/Program Files/KDiff3/kdiff3.exe"[diff]    tool = kdiff3    guitool = kdiff3[difftool "kdiff3"]    path = "/mnt/c/Program Files/KDiff3/kdiff3.exe"[core]    autocrlf = true

Then I encountered an error:

Opening of these files failed- [filename].[extension] (A)

The program window opened correctly, but only the right side file (B) was displayed.

The error is repeatable every time. What can cause this error?