Yes, it disappears from the tray. XP only as far as I can work out. It comes back after an update. No-one knows why it does this : it just does. Another puzzling McAfee quirk.
The important thing is that McAfee is still humming away in the background; all that's happened is the icon has decided to go AWOL.
It is my understanding that this is a "Normal" occurance. Due to the implemented change-procedure in regards as to how Updates/Upgrades are Downloaded/installed without a "Restart required,in the 12.8.856 Version. I cannot recall the particular thread, but "Dougtk" explained this to another Community Member sometime back in October/2013 or sometime there-about.
I also observed the identical occurance, while my PC was idle,and Monitor had yet to "Go to sleep"
Having said this, I simply rely on "Automatic Updating" and normally would not have seen this occurance.
In my instance, I observed the McAfee Icon with the "Gray" Arrow spinning, as it was Downloading the daily Update, then it briefly dissappeared and returned. After hovering my mouse over the icon, it informed me that it was "Installing Updates" Upon completion, the McAfee Alert Prompt displayed that the latest McAfee Updates had been installed.
After a few seconds, as expected the prompt disappeared ...and upon checking my "About" in McAfee Security Center...It indeed had installed the current daily Update. I am pleasantly pleased that this occurs in the same manner, when an Version Upgrade occurs...minus the normal "Restart Prompt" experienced in the 2012 Version-11.6.
On very rare occasions, I experience a prompt from the Windows Security Center not recognizing the update. Which I have previously posted in another thread in regards to this rare occurance. Having said this...This is a Microsoft related issue, not McAfee.
You can resolve this issue by simply restarting, or use the procedure I posted.
As Hayton stipulated...there is no reason to be concerned.