I'm not going to check now because I'm not on my computer with maple, but I'm 90% sure that this isn't a FJ-associated issue.
Try going to the top of a high monster map (maybe somewhere in Ludi?), and fall all the way down at once. You'll likely encounter the same problem. Thus, your guess in the detailing of the problem is correct, falling and FJ are related.
This has happened in most servers I've played, and I guess (especially when that there's a lot of spawn and drops), that there's a delay in the server relaying all that information to the client, and vice versa. You see this problem with FJ + Haste because to my knowledge it's the fastest skill combination available to any job to cross maps. I don't think you can fix this issue. It's basically just a smaller-scale, momentary server lag.