I'm not an insider so I can't speak with confidence about the inner workings of the share trading mechanisms, and I generally try to stay away from conspiracy theories, but I do have personal experience that doesn't correspond with the official line.
A long time ago, before the days of CHI, I attempted to sell some shares on the'open' market. The bids amounted to about three times the quantity I was to sell. There had not been a trade for about 10 minutes. So, being a bit desperate to sell, I put in my sell order. What happened was that ALL the bids disappeared on me submitting my order, without a single share changing hands.
Clearly, in a transactionally safe system I should have been successful. In reality the bidder(s) got advanced warning of my intention to sell.
In my experience, this sort of behaviour continues today.
As one who has spent a lot of time designing distributed processing systems I find it difficult to understand why this behaviour is allowed to continue.
