Hmm, I've never had this problem before.
When it disappears, just hit 'W' on your keyboard to bring it back.
You say can only see it in your Perspective view? Are you sure your not talking about the Compass?
Sounds odd!
www.stevenegan-cgi.com
"Your weapons are no match for ours! People of Mars, surrender!"
"Um, this isn't Mars. This is Earth."
"Earth? Earth-with-nuclear-weapons Earth?"
"Yes."
[long pause] "Friend!!"