Having stickySessionForce* mod_cluster set to true by default IMHO defeats the whole purpose of using HA, if the client is going to end up with error returned anyway.
I propose if we are running AS7 the default should be false and failover should be just transparent and with ASYNC having a stale session is better than returning an error. I guess the configuration should keep in mind that mod_cluster is primarily used with HA clusters. This makes most sense with standalone Tomcat only.
*Return an error when the request cannot be routed to the right node.