Do you know how this can happen?
The distance at which the sequence can be locked in can be extended somewhat by requiring aircraft departing from close by airports to obtain their feeder fix time before they depart. The flow will then lock that aircraft into the sequence and is able to then lock in the other aircraft around it. Those aircraft are usually departing from aerodromes that aren't very busy and they can usually takeoff whenever they want to make sure they meet that time. You just couldn't get that from airports like Sydney, they may have to wait in a queue to cross a runway, then for an aircraft to land then the next 4 aircraft in front to take off.
The sequence doesn't become stable until all the aircraft that will land before you are either airborne, or have phoned up the flow and locked in their feeder fix time.
I know it's not the first position most pilots would want to famil on when they visit a TCU. Director is much more exciting. But flow control is a bit of a dark art, and you're questions haughtney would be answered in one visit. I highly recommend it it. It's too complicated and drawn out to explain it on a forum.