When a grouping-handler is added to the hornetq-server section, the AS7 server starts with an error:

15:18:14,521 ERROR [org.jboss.as.controller.management-operation] (ServerService Thread Pool – 52) JBAS014613: Operation ("add") failed - address: ([
("subsystem" => "messaging"),
("hornetq-server" => "default"),
("grouping-handler" => "group-handler-test")
]) - failure description: "JBAS011637: A child resource of type grouping-handler already exists; the messaging subsystem only allows a single resource of type grouping-handler"

The error is misleading as there is only 1 grouping-handler and the server runs fine.