Why local ports increased so much when update from 1.0.15 to 1.2.8

Recently, I updated nginx from 1.0.15 to 1.2.8, and find that the ports(shown by ss -s) increase much as below:

nginx/1.0.15
Total: 21696 (kernel 22773)
TCP: 111474 (estab 21422, closed 86149, orphaned 3803, synrecv 0, timewait 86145/0), ports 1417

nginx/1.2.8
Total: 21579 (kernel 22349)
TCP: 57466 (estab 21295, closed 32654, orphaned 3438, synrecv 0, timewait 32652/0), ports 11239

I updated nginx in order to use the ngx_http_upstream_keepalive module, most ports are used by nginx to connect with squid(port:8081):

(nginx/1.2.8) netstat -anp | awk '$5 ~ ":8081"' | grep -i time_wait | wc -l
10227
(nginx/1.0.15) netstat -anp | awk '$5 ~ ":8081"' | grep -i time_wait | wc -l
15

Is there any change that make nginx make lots of connections with squid and occupy so much ports?