one project,many tomcat occurred session replaceed

1) one spring web project：DemoWeb.war
2) two tomcat (port: 8080/8081)
3) spring-session-redis(Using spring-session-redis to realize distributed session.)

deployed:

setp1: useing this url http://ip:8080/demo/ login successful;

setp2:access menu url http://ip:8080/demo/menu successful;

setp3: open new tab in browser, and input http://ip:8081/demo/menu (port is difference), enter；

I don't login the 8081 server, why the http://ip:8081/demo/menu can access successful??