mod_cluster + mod_proxy_wstunnel doesn't work - all workers are in an error state

Reported by KooV <coolseed hotmail.com];

h3. Description of problem:
mod_cluster + mod_proxy_wstunnel causes segfault

LoadModule proxy_cluster_module modules/mod_proxy_cluster.so
LoadModule cluster_slotmem_module modules/mod_cluster_slotmem.so
LoadModule manager_module modules/mod_manager.so
LoadModule advertise_module modules/mod_advertise.so

MemManagerFile /software/httpd/cache/mod_cluster

Listen 192.168.0.81:6666
<VirtualHost 192.168.0.81:6666>
    <Directory "/">
        Require all granted
    </Directory>

    KeepAliveTimeout 60
    MaxKeepAliveRequests 0
    ManagerBalancerName mycluster
    EnableMCPMReceive
    ServerAdvertise Off
</VirtualHost>

<Location /mc>
    SetHandler mod_cluster-manager
    Require all granted
</Location>

LoadModule lbmethod_byrequests_module modules/mod_lbmethod_byrequests.so
#LoadModule proxy_balancer_module modules/mod_proxy_balancer.so
LoadModule proxy_wstunnel_module modules/mod_proxy_wstunnel.so

<Proxy balancer://TEST_WS>
    BalancerMember ws://192.168.0.81:8080 route=node11
    BalancerMember ws://192.168.0.82:8080 route=node21
    ProxySet stickysession=JSESSIONID|jsessionid
</Proxy>

RewriteEngine On

RewriteCond %{HTTP:Connection} upgrade [NC]
RewriteCond %{HTTP:Upgrade} websocket [NC]
RewriteRule /jboss-websocket-hello/(.*)               balancer://TEST_WS/jboss-websocket-hello/$1 [P,L]

If you request websocket open, segfault will always occur.