EJB client from EAP 7.0 is sometimes authenticated as $local even when it is forbidden

when running EJB client from EAP 7.0 (EJB client 2.1.x) or the 7.1 legacy client (3.0.x), against EAP 7.1.0.ER3 (and newer) server on the same machine (with the same standalone.xml), even when the client has explicitly forbidden LOCAL authentication, he is sometimes (intermittently) authenticated as the user $local.
This does not happen when the server is EAP 7.1.0.ER2, or when using EJB client 4.x.

Impact: the client is intermittently authenticated as a different user than expected, this also makes invocations randomly fail, because the $local user typically isn't assigned to authorization roles which are typically required for invocations of some methods. Or the other way around, this could actually elevate the user's privileges in some cases.