Notice in error log if using disabled language as admin language

In my case, I have three languages(chan-s, chan-t and english) on my site, chan-s and chan-t are enabled for front-end use. But we need use english as admin language, so we use admin_lanuage module as solution. Everything looks good, but i found some notice in our log.

Notice: Undefined index: en in admin_language_language_init() (line 565 of /var/www/gousa/sites/all/modules/admin_language/admin_language.module).