So the best bet is to get it going on the ground to get a decent position fix and then it ought to be ok?
That is true for good many GPSs, actually. However I found the Ipad2/3G losing its fix in the air, having got it prior, and that is weird.
However if you switch apps, and so turn off searching for GPS - you will be back to the start of getting an initial fix again.
That might explain what I was seeing. A crap design though.