如何在Go模式下调试gofmt命令

Here is my config:

(add-hook 'before-save-hook 'gofmt-before-save)
(setq-default gofmt-command "gofmt")

When I press M-x gofmt I get the next message in the Messages buffer:

Wrote c:/Users/andre/AppData/Local/Temp/gofmtXYhFv6.go
Calling gofmt: gofmt (-w c:/Users/andre/AppData/Local/Temp/gofmtXYhFv6.go)
Applied gofmt

But my source file is still unformatted. I am using emacs on Windows. How can I find the reason of problem ?