Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version go1.10 windows/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\HuangTao\AppData\Local\go-build
set GOEXE=.exe
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOOS=windows
set GOPATH=E:\GoProject
set GORACE=
set GOROOT=C:\Go
set GOTMPDIR=
set GOTOOLDIR=C:\Go\pkg\tool\windows_amd64
set GCCGO=gccgo
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=C:\Users\HuangTao\AppData\Local\Temp\go-build137051418=/tmp/go-build -gno-record-gcc-switches

What did you do?

package main

import (
	"fmt"
	"net/url"
)

func main() {
	u := "https://www.example.com?q=5a545a42302f49252189&delivery_id=%DL%&app=%MA%&did=%MI%&channel=WD&slot_id=__clickid__&idfa=%MI%"
	ul, err := url.Parse(u)
	if err != nil {
		panic(err)
	}
	fmt.Println(ul.Query().Encode())
}

What did you expect to see?

q=5a545a42302f49252189&delivery_id=%DL%&app=%MA%&did=%MI%&channel=WD&slot_id=__clickid__&idfa=%MI%

What did you see instead?

channel=WD&q=5a545a42302f49252189&slot_id=__clickid__

the keys (delivery_id, app, did) are lost.