Comment 27 for bug 1302462

Do the following :

sudo mousepad /etc/NetworkManager/NetworkManager.conf

and change :

[ifupdown]
managed=true

The default value is false, but it seems that if when the system starts the network is not yet ready the applet will not be displayed

if you set the value to true, it solves the problem.

PS : depending on your distribution the file may be called nm-system-settings.conf instead of NetworkManager.conf