Just as another data point to this, it happens to me too. (No, I don't have a log atm. )
One consistent scenario is thus:
Night Elf in Twilight Highlands.
Using Archbuddy to level from 84-85, and got into a bad area.
It can't get back to the corpse (at Humbolt Conflagration).
The graveyard for Humbolt is on a mountain, and Humbolt is in a valley, and apparently, there is no ground path back. It gets "as close as it can" on the mountain edge, and just sits there while in Wisp form.
There is at least one other 'ruins' site in Twilight Highlands configured similarly, but I can't recall its name atm.
I can understand what the problem probably is...
the Night Elf wisp form "can fly", but is not mounted. The code that probably detects for the "dead, but can fly detection" is looking for a 'mounted' flag.