My roundrobin setup is not roundrobin-ing

My config file is below. By way of explanation, I am using an acl to redirect urls that start with /cas to my single signon server. Everything else goes to my tomcat servers. If I run ab without using a url that goes to /cas, then everything roundrobins fine. However, my applications redirect to /cas which in turn redirects them back to the haproxy cluster once authenticated. When I go through this process, haproxy always puts the session on the first tomcat instance. Is there a way for me to debug how haproxy/my config is making decisions on which backend to use for a new session?

Thanx,
LES

	log 127.0.0.1 local0 info
	maxconn 25000
	stats socket    /tmp/haproxy.sock level admin
defaults
	log global
	clitimeout 60000
	srvtimeout 300000
	contimeout 4000
	retries 3
	option redispatch
	option httpclose
	option abortonclose

listen http_https_redirect *:80
	mode http
	acl stunnel src 192.168.xxx.zzz/32
	redirect prefix https://erp.barnhardt.local unless stunnel

frontend tomcat *:81
	mode http
	acl ssorequest path_beg /cas
	use_backend sso if ssorequest
	default_backend tomcat_cluster

backend sso 
       	mode http
       	balance roundrobin
       	option forwardfor except 0.0.0.0
       	reqadd X-Forwarded-Proto:\ https
       	cookie SERVERID insert indirect
       	option httpchk HEAD /check.html HTTP/1.0
       	server sso 192.168.xxx.zzz:18080 cookie A check

backend tomcat_cluster 
	mode http
	stats  uri /haproxy?stats  
        stats enable
	balance roundrobin
	option httplog
	option forwardfor except 0.0.0.0
	reqadd X-Forwarded-Proto:\ https
	cookie SERVERID insert indirect
	option httpchk HEAD /check.html HTTP/1.0
	server tomcat01-instance1 192.168.xxx.xxx:8080 cookie A check port 8081 inter 2000
	server tomcat01-instance2 192.168.xxx.xxx:18080 cookie B check port 18081 inter 2000
	server tomcat02-instance1 192.168.xxx.yyy:8080 cookie C check port 8081 inter 2000
	server tomcat02-instance2 192.168.xxx.yyy:18080 cookie D check port 18081 inter 2000
	
	server bkup-tomcat01-instance1 192.168.xxx.xxx:8080 cookie A check port 8080 inter 2000 backup
        server bkup-tomcat01-instance2 192.168.xxx.xxx:18080 cookie B check port 18080 inter 2000 backup
        server bkup-tomcat02-instance1 192192.168.xxx.yyy168.60.157:8080 cookie C check port 8080 inter 2000 backup
        server bkup-tomcat02-instance2 192.168.xxx.yyy:18080 cookie D check port 18080 inter 2000 backup