Docker 1.7 docker exec now launchs as root unlike docker 1.6 1.5

in docker 1.5 and 1.6 “docker exec container cmd” would launch the cmd as the user that was specified in either the docker create/run command or in the dockerfile used to create ‘container’. Now it runs as root unless the user name is specified in the docker exec command.

Is there a way to revert to pre 1.7 behaviour ?

I very much liked the idea that containers could exist in which root could never run.
It feels like a feature vanished!