What steps will reproduce the problem?

lucky(~/src/woo) % echo "package woo;var      format  =    bool" > woo.go
lucky(~/src/woo) % echo "package woo;var      format  =    bool" > _woo.go
lucky(~/src/woo) % go list -f '{{ .GoFiles }}'
[woo.go]
lucky(~/src/woo) % go fmt 
_woo.go
woo.go

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

go list says that there is one file in this project, _woo.go is ignored correctly.

go fmt touches _woo.go, which is incorrect.

Please use labels and text to provide additional information.