This is similar to MODCLUSTER-328, but in regards to ; instead of ?.

mod_cluster does not recognize ; as a delimiter when checking the request context. Thus with no trailing slash on index page requests, it treats ;jsessionid as part of the request context and tries to check the balancer for a deployed context of /helloworld;jsessionid=..., which doesn't exist and 404s. Adding the trailing slash, mod_cluster can properly delimit this and then sees the context (so /helloworld/;jsessionid=... works just fine).