I don't believe that the plunge was intended.
The intention was to manipulate the market in order to trade on the change.
Unfortunately, other traders and computer trade systems have become wise to this system and will also attempt to trade with the manipulation.
This results in a cascade of trades all in the same direction from a positive feedback loop.
This has resulted in the "brittle" market.
Since it is already against the rules to manipulate the market, and nearly impossible to prove, it's going to take something else to make this kind of action stop.