iptables resetted every 60 minutes

Hi, 

I have WNR3500L router with DD-WRT v24-sp2 (08/12/10) mega(SVN revision 14929). The "issue" I have is that iptables is resetted every 60 minutes. 
If I manually add a new rule by sshing to the box and typing the "iptable -A" command, it will be removed after 60minutes. 
Why ? How is this reset triggered ? Is it possible to disable this "feature" ? 

In the message file, every hour, I find a bunch of lines of module unload/load + restart of the process_monitor+restart of WLAN daemon. 
The first line is always "Feb 8 21:01:34 plouf user.info syslog: vpn modules : vpn modules successfully unloaded" 

# grep "process_monitor successfully started" messages 
Feb 8 17:01:40 plouf user.info syslog: process_monitor successfully started 
Feb 8 18:01:36 plouf user.info syslog: process_monitor successfully started 
Feb 8 19:01:41 plouf user.info syslog: process_monitor successfully started 
Feb 8 20:01:37 plouf user.info syslog: process_monitor successfully started 
Feb 8 21:01:34 plouf user.info syslog: process_monitor successfully started 

I can't find anything in the crontab. 

Can someone try following the command (syslog must be enabled...): 

And tell me if I'm the only one with this periodic reset or if it's a normal behavior of the system.

Any idea? 
Regis