network device name is changed by itself

I make use of a Ubuntu - arm, uname -a

Linux arm 3.7.8-x8 #1 SMP Sat Feb 16 04:15:13 UTC 2013 armv7l armv7l armv7l GNU/Linux

I have 2 USB WiFi user interfaces that are called wlan0 and also wlan1 on /etc/udev/rules.d/70-persistent-net.rules

I run a manuscript on each start - up that does:

ifdown wlan0 
rm /var/run/wpa_supplicant/wlan0
ifup wlan0
wpa_supplicant -B -Dnl80211 -iwlan0 -c/etc/w.conf

ifdown wlan1
rm /var/run/wpa_supplicant/wlan1
ifup wlan1
wpa_supplicant -B -Dnl80211 -iwlan1 -c/etc/w2.conf

occasionally among the user interface is called as rename5 whereas the various other user interface is called according to the 70-persistent-net.rules.

Could any person clarify why it is called rename5 as opposed to wlan0 or wlan1 and also just how can I protect against that point to take place?