The strangest thing I ever saw was pre-market NQ on 8/24 last month. Volume just piling up at the circuit breaker level (3992-ish?) and over 15 levels of Bid totally empty below.
Back during the SGX A50 party days in June/July I was actually able to exploit this as a gimmicky edge. China markets were so volatile that there was a week the A50 contract would hit both limit downs (and even limit up at one point). I'd precalculate the circuit breaker levels and mark them on my chart and as price approached the limit down I'd just sell market before it started piling up - waiting the 15 mins until it exploded downwards. The problem though was you couldn't send limit buy orders as a target because the exchange refused them for being past limits. So by the second time I had changed my orders around to be MIT orders. Even though I was able to pick up some "free money" it wasn't nearly the full length of the move when the circuit breaker was released because the retrace was pretty damn fast.
...said by people who teach, rather than do themselves.