Confusion with json htmlescaped and utf-8

I’m confused with json and utf-8.
I have two environments, one in local where I changed and tried the hugo version from 0.26 to 0.27.1 with either go1.8.1 go1.8.3, go1.9 and I still get my characters not escaped.

hugo env

Hugo Static Site Generator v0.28-DEV linux/amd64 BuildDate: 2017-09-20T14:48:47+02:00
GOOS="linux"
GOARCH="amd64"
GOVERSION="go1.8.1"

Sant\u00e9 et M\u00e9decine douce
and one in development

hugo env

Hugo Static Site Generator v0.28-DEV linux/amd64 BuildDate: 2017-09-12T13:33:05+02:00
GOOS="linux"
GOARCH="amd64"
GOVERSION="go1.8.1"

or my characters are correctly escaped
Santé et médecine douce

Would there be a regression ?

Thanks

For information, the transition to version 0.28 still does not correct the problem.