Well, seems that other application (maybe Automatic Task Killer https://play.google.com/store/apps/details?id=biz.stachibana.TaskKiller) is killing the icon on system tray. avast is running if I check the task manager.
If I open avast, uncheck to hide the icon, answering yes and than enabling the icon again, the icon is restored.
Until next killing.
Is there a way to harder/strength the icon on system tray?
Are you using ICS? If so, wait for the next release, there will be certain fix for ICS icon presence so we will see afterwards.
Filip
Yes, I’m using the Google 4.0.2 maguro official release (http://code.google.com/intl/pt-BR/android/nexus/images.html), rooted although.
OK, wait for the next release then 
Filip
Thanks again Filip.
I know we won’t support non official releases, but I suppose it will work in CyanogenMod (nightly/Kung) stream, won’t it?
It should work more or less fine in CM.
How is the icon problem doing? Still disappearing?
Filip
No. Working fine on Google official stock image 4.0.4.
Glad to hear that
Filip