Doubts on roundrobin loadbalance method (no replies)

hi，all：
I'm using haproxy-1.5.14. When i change the server health state in turn（set server app_tomcat_standalone/xxx health up/down），some servers will not be forwarded to. Eg: I have 80 servers in backend app_tomcat_standalone.Then I turn off all the servers(set server app_tomcat_standalone/xxx health down).After two seconds, I ture on all the servers.Finally, I send 80 requests.From the stats page, I see that some servers got two sessions and some got zero. I'm using roundrobin, it should be only one session for each server. Is that Ok? My environment is
OS:

Haproxy Config:
....80 servers.

I found this in the haproxy configuration file

Does that cause the problem? Looking forward for your reply. Thanks~


hu.zhang@dev.bessystem.com