It's normal if your order is routed to PERT as the MM. They will show the best offer. Your 1000 @ 2.51 bested the 51,500 @ 2.55 so they were obligated to show it. Once your order was removed or cancelled, the 51,500 @ 2.55 was probably the next best offer they had in the stack. That's how it's supposed to work.