I had the same issues as the OP also.
After installing Avast 5 I noticed, after restarting the PC, that I was missing a few system tray icons.
The most notable ones were Avast, FD-ISR, Prevx, and a few of my personal programs that run at Windows start up.
After further reboots, I lost more icons in the system tray each time. I believe I rebooted about four times.
I was then down to one or two icons when I normally have ten or eleven.
I used FD-ISR to revert back to an earlier snap shot and I have my system tray icons back.
I am back to using Avast Home 4.8 and will continue to watch this thread for further developments on this issue.
Thanks.