Ttyjfyk

I have Beaglebone Black with installation of Debian 7.11 Wheezy

I have network which is created from Beaglebone and the Beaglebone IP address is set to be static: 192.168.20.1

This is my /etc/network/interfaces file:

# The wireless network interface
#allow-hotplug wlan0
auto wlan0
#iface wlan0 inet dhcp
# wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf
iface wlan0 inet static
 address 192.168.20.1
 netmask 255.255.255.0

When I use static IP 192.168.20.1 I also run hostapd and isc-dhcpd-server services, for can create network with which users can connect to beaglebone:
My isc-dhcp-server is set to put IP address from 192.168.20.3-254
This is my dhcpd.conf file:

subnet 192.168.20.0 netmask 255.255.255.0 
 range 192.168.20.3 192.168.20.254;
 option broadcast-address 192.168.20.255;
 default-lease-time 600;
 max-lease-time 7200;

I found on deamon.log file for some reason dhclient is probably change the beaglebone IP address

Mar 20 11:36:01 smartgrow dhclient: DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 4
Mar 20 11:36:01 smartgrow rc.local[717]: sudo: unable to resolve host smartgrow
Mar 20 11:36:02 smartgrow dhclient: DHCPREQUEST on wlan0 to 255.255.255.255 port 67
Mar 20 11:36:02 smartgrow dhclient: DHCPOFFER from 192.168.20.1
Mar 20 11:36:02 smartgrow dhclient: DHCPACK from 192.168.20.1
Mar 20 11:36:02 smartgrow samba[2929]: Reloading /etc/samba/smb.conf: smbd only.
Mar 20 11:36:02 smartgrow dhclient: bound to 192.168.20.5 -- renewal in 281 seconds.
Mar 20 11:36:04 smartgrow ntpd[864]: Listen normally on 7 wlan0 192.168.20.5 UDP 123

EDIT: The thing which dhclient make something on /etc/rc.local is run on that script

#!/bin/sh

if [ -f /etc/wpa_supplicant/wpa_supplicant.conf ] # If file exist
then
 version=$(sudo /bin/cat /home/network/option.gse)
 if [ "$version" = "static" ]
 then
 sudo cp /home/scripts/user /etc/network/interfaces
 else
 sudo cp /home/scripts/dynamic /etc/network/interfaces
 fi
else
 sudo cp /home/scripts/static /etc/network/interfaces
fi

/etc/init.d/isc-dhcp-server stop
/etc/init.d/hostapd stop

ip addr flush dev wlan0
ip link set wlan0 up

/etc/init.d/networking restart

ip=$(/sbin/ifconfig wlan0 | grep 'inet addr' | cut -d: -f2 | awk 'print $1') # Get IP address for wlan0
case "$ip" in
 192.168.20.* | "")
 
 sudo cp /home/scripts/static /etc/network/interfaces
 /etc/init.d/hostapd stop
 ifconfig wlan0 192.168.20.1/24
 ip addr flush dev wlan0
 ip link set wlan0 up
 /etc/init.d/networking restart
 sleep 10
 wifis=$(iwlist wlan0 scann ;;
 *)
 grep ESSID ;;
esac

/etc/init.d/samba restart

ip=$(/sbin/ifconfig wlan0 | grep 'inet addr' | cut -d: -f2 | awk 'print $1')
mask=$(/sbin/ifconfig wlan0 | awk '/Mask:/ print $4; ')
gateway=$(ip route show default | awk '/default/ print $3')

My questions is:
Why is something (dhcp) change my static IP address? And how to resolve that, when I put static IP address to not be changed?