Fix for MODCLUSTER-391 in fact in the branch httpd cores :-(

I was just using:
CreateBalancers 2
<Proxy balancer://mycluster>
  BalancerMember ajp://127.0.0.1:8009
#ProxySet failonstatus=405,401
</Proxy>

got a core in httpd-2.4.2 so the fix should help.