Also added a test to ensure the behavior.

Fixes #14150

Change-Id: Ib3ee9fdae59826fa594ce1be3c49b51d740b56eb
Reviewed-on: https://go-review.googlesource.com/19915Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>