Centos – why nginx holds file descriptions of logs

on Red Hat Enterprise Linux Server release 6.6 (Santiago)
nginx version: nginx/1.0.15

I use common nginx logrotate config, logrotate works fine and nginx creates new log file like access.log or error.log

# cat /etc/logrotate.d/nginx 
/var/log/nginx/*log {
    daily
    rotate 4
    missingok
    notifempty
    compress
    sharedscripts
    postrotate
       /bin/kill -USR1 $(cat /var/run/nginx.pid 2>/dev/null) 2>/dev/null || :
    endscript
}

However, one time my free space became low and after a while I found that nginx keeps file descriptors of deleted files. Only way to free space on the server is to restart nginx thereby free file descriptors.

Any ideas?

>     [srv2 nginx]# logrotate -f  /etc/logrotate.d/nginx 
>     [srv2 nginx]#  lsof +L1
>     COMMAND    PID        USER   FD   TYPE DEVICE SIZE/OFF NLINK NODE NAME
>     vmtoolsd  1125        root    3u   REG  253,3     4240     0   45 /tmp/vmware-root-2883746505/vmware-apploader-1125.log (deleted)
>     nginx    38748 nginx    2w   REG  253,4  1370362     0  674 /var/log/nginx/error.log.1 (deleted)
>     nginx    38748 nginx    4w   REG  253,4  1370362     0  674 /var/log/nginx/error.log.1 (deleted)
>     nginx    38748 nginx    5w   REG  253,4        0     0  220 /var/log/nginx/access.log (deleted)
>     nginx    38748 nginx    6w   REG  253,4    41819     0  693 /var/log/nginx/localhost.access.log.1 (deleted)
>     nginx    38749 nginx    2w   REG  253,4  1370362     0  674 /var/log/nginx/error.log.1 (deleted)
>     nginx    38749 nginx    4w   REG  253,4  1370362     0  674 /var/log/nginx/error.log.1 (deleted)
>     nginx    38749 nginx    5w   REG  253,4        0     0  220 /var/log/nginx/access.log (deleted)
>     nginx    38749 nginx    6w   REG  253,4    41819     0  693 /var/log/nginx/localhost.access.log.1 (deleted)
>     nginx    38750 nginx    2w   REG  253,4  1370362     0  674 /var/log/nginx/error.log.1 (deleted)
>     nginx    38750 nginx    4w   REG  253,4  1370362     0  674 /var/log/nginx/error.log.1 (deleted)
>     nginx    38750 nginx    5w   REG  253,4        0     0  220 /var/log/nginx/access.log (deleted)
>     nginx    38750 nginx    6w   REG  253,4    41819     0  693 /var/log/nginx/localhost.access.log.1 (deleted)