Zyg, Your question....
I have never head of it, my response would be to do what you already did and call a few diffrent Brokers and simply ask, in
a small Penney it would sort of have an effect, I wonder at the end of the day when they are reconciling everything if that is
where some of the balances looks like it's in a fifth position but not really trading there?
Best of luck here, I hope it works for you guys, just some things are bothering me, but like I said would jump back in if things change.
MC