Should containers inherits the group/gid from the image configuration?

From https://github.com/opencontainers/image-spec/blob/master/config.md#properties

User string, OPTIONAL

The username or UID which is a platform-specific structure that allows specific control over which user 
the process run as. This acts as a default value to use when the value is not specified when creating a 
container. For Linux based systems, all of the following are valid: user, uid, user:group, uid:gid, 
uid:group, user:gid. If group/gid is not specified, the default group and supplementary groups of the 
given user/uid in /etc/passwd from the container are applied.

the scenario is simple, what happens in the following case:

User 1000:100

and the container runtime just specifies to run the container as user 3000? Should it inherit the group from the image configuration? it shoiuld run the container as 3000:100. Right now, in docker for instance, that's not the case, it'll end up running 3000:0 (0 being a default).

/cc @simo5 @vbatts
xref https://github.com/openshift/origin/issues/8618

Start with the linked OCI image-spec config.md section and the referenced OpenShift issue. Compare the stated User value semantics with Docker's behavior for a runtime user override. Done means the inheritance question has a decided, documented specification outcome; no repository file or test is named in the issue.