Sorry to update this, I didn't want to start a new thread.
Any news on this bug and how to fix it. This is now happening on my screen quite regularly, from all airports within my reception area, i.e Heathrow, Gatwick, Luton and Stansted.
The only way to get the aircraft back on the map is to deselect and select "process hardware flights", so that it refreshes the map. this will fix the problem for awhile, then it'll re-occur later until I repeat the process. I have tried the box on my laptop, happens on that too.
Desktop specs:
HP Pavilion desktop
Intel Quad Q6600 @ 2.4Ghz
6GB ram
Nvidia Geforce 8500GT 512mb graphics
Windows 7 Ultimate x64.
I've attached a latest screen shot highlighting two aircraft with a (globe) ADS/B, but not visible on the map. They have taken-off from Heathrow and are in close vicinity of the airport.