sad to say that it is true... when i was a cm, i did an in-depth tour of the HM, and my trainer told us about a guy that climbed out in leota's room, and was headed to Leota's table.
what guests don't realize is that they are actually many feet above the 'floor' of the attraction, and the area around leota's table was a drop off to the bottom.
now there is a wire grill/cage that surrounds leota's table 'just in case' but the area behind the doombuggies is still a drop off (over a slight wall).
whether this is 100% true or not, i can't say, only because i didn't see it with my own eyes, but having heard it from sources, and then being told on my HM tour as a CM, really made me believe it.
the sad thing is that these guests are on vacation, not thinking, and don't think you can 'get into trouble' at disney...