Yeah, I've always found it odd, but I can run heavy sometimes. The thing is, my family is three so when we do the regular line, we tend to stage for the first three seats, but I've had visits to UOR where I would be good one day and then on another day, I would be told to switch.
I think that is part of the reason we will do single rider more often as we can save time and we never know if we will truly sit together each ride.
It did freak me out a little the first time it happened, but now that my daughter knows the park well and she even suggest single rider these days.
I have noticed that the staff at FJ seem to err on the side of safety, which is a good thing...I am not sure how they tell, but they seem to be looking at indicators (I assume lights) at the front of the benches and then again when they mess with buttons on the side of the restraints...they seem to be quick about getting folks to switch since it is a magic carpet load and when I am asked to switch, it is at the last check...