go: cmd/go: go test -cover fails when xtest imports main which imports package being tested

I’m using

 go version
go version go1.6 darwin/amd64

Go env

$ go env
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/hvn/Github/gomeo"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GO15VENDOREXPERIMENT="1"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fno-common"
CXX="clang++"
CGO_ENABLED="1"

when I run go test with coverage (-cover), it failed to import the package that it was okay when I ran test without -cover. I added debug log to compile and rebuild go, I got those log:

compile: LOG: handling import: git.example.com/repo/t-p
compile: LOG: alldir: $WORK
compile: LOG: alldir: /Users/hvn/Github/gomeo/pkg/darwin_amd64
compile: LOG: checking file $WORK/git.example.com/repo/t-p.a
compile: LOG: checking file /Users/hvn/Github/gomeo/pkg/darwin_amd64/git.example.com/repo/t-p.a
./kickkick.go:7: can't find import: "git.example.com/repo/t-p"

AFAIU, it should import from /Users/hvn/Github/gomeo/pkg/darwin_amd64/git.example.com/repo/_test/git.example.com/repo/t-p.a, no?

https://github.com/golang/go/blob/release-branch.go1.6/src/cmd/go/test.go#L697

    // That is, if the package under test is unicode/utf8,
    // then the normal place to write the package archive is
    // $WORK/unicode/utf8.a, but we write the test package archive to
    // $WORK/unicode/utf8/_test/unicode/utf8.a.
    // We write the external test package archive to
    // $WORK/unicode/utf8/_test/unicode/utf8_test.a.

I removed this line, rebuilt go and it worked https://github.com/golang/go/blob/release-branch.go1.6/src/cmd/go/test.go#L850