I also lose ground vehicles when I get within 2k or so, so I sort of have to shoot at where I last saw them. The fleet dissapears when I fly near it, and sometimes it stays gone, sometimes it sort of flickers in and out of existance. I can still see the wake of the ships, and sometimes the hull, but not the decks.
It happens to buildings on bases to- if I want to strafe something I have to get it in my sights before I get within 1k or so, or it will dissapear. Buildings reappear when I fly up and I'm exactly over them, if I move away from straight over one it dissapears. Hangers, ack, everything- it all dissapears. I can BOMB ok, it never dissapears when I'm in a buff and pretty high above the base.
As I said before, this doesn't happen in the new version (DX8 beta 12)- only in the "normal" AH. However, the game runs a lot smoother in the normal mode, it gets kinda jaggy in the beta version.