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 GOEXE=.exe
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOOS=windows

What did you do?

Creating one type that is alias to []byte will not trigger the Marshal, but triggers the Unmarshal, like:

type MyType []byte

type StructJSON struct {
	Name MyType
}

func (d *MyType) MarshalJSON() ([]byte, error) {   // << Never will be triggered
}

func (d *MyType) UnmarshalJSON(data []byte) (err error) { // << Working :)
}

See the demonstration at https://play.golang.org/p/FHOMVOq1oDD

What did you expect to see?

I expect that the same result of UnmarshalJSON. In the demonstration the message of Marshal is working should be displayed.

What did you see instead?

The MarshalJSON() are not beginning triggered and don't have the same behavior of UnmarshalJSON.