What is a transaction, that has "virtual" in the place of it's ID?

The account history log is based on operations. Most events are directly triggered by user operations - for example, if user A sends funds to user B, user A creates a transfer_operation with the amount to send and the IDs of users A and B as parameters.
Some events are not directly triggered by user operations, though, or the connection between operation and event is not obvious. Such events are represented by virtual operations. For example, when an order is filled, a virtual fill_order_operation is created by the blockchain logic.

So here is my question: what happens if the market gaps when volatility becomes extreme? Isn't there a chance that pegs such as BitUSD break in the event of a black swan?

A black swan *is* the situation when a bitasset becomes undercollateralized. When that happens, the settlement guarantee that defines the peg is replaced by a fixed exchange rate bitasset -> BTS, so essentially the bitasset is pegged to a fixed amount of BTS instead of its "real" counterpart.

This has already happened to some bitassets, like SEK, RUB, KRW, and more recently GOLD and SILVER. We are currently deploying a method to re-collateralize bitassets after a black swan to make them usable again.

Make sure "enable-stale-production = false" is set in your config.ini (on all nodes).

I think our bitCNY problem is caused by people in China moving from CNY into (other) cryptos, using bitCNY and BTS as intermediates. I. e. CNY -> (via magicwallet) -> bitCNY -> (via forced settlement) -> BTS -> BTC (or other cryptos).

That would explain why CNY:bitCNY is trading above the peg, while at the same time BTS:bitCNY is trading below - if there was real demand for bitCNY, people would buy it on the DEX. In reality, people are dumping bitCNY for BTS either on the DEX or via forced settlement.
I think changing the settlement offset will not change this situation - it would only continue on a different level. (It seems the proposal has been accepted by now - we will see if it helps.)

BTS has been in an uptrend during the past couple of days. It is normal that during a BTS uptrend bitassets trade below the peg, because the settlement delay means that the bitasset is actually pegged to the expected price one day in the future.

Some people are arguing that the price feed is off, because the indirect price CNY->bitCNY->BTS doesn't match the feed price. I think that argument is invalid because of the abovementioned dependency between the bitCNY->BTS price as seen on the DEX and the feed price. The feed price must not be calculated as a function of the internal trade price, because that would create a feedback loop, and feedback loops are inherently unstable.​

Good news, but please note that bitKRW is currently in global settlement. After the next hardfork (planned for Dec 08), witnesses can publish a price feed for KRW again, which should revive the asset.

I am a big shorter, how can I scam the DEX users?

1. You sell bitCNY and promise that holders can settle their bitCNY for an equivalent amount of BTS within 24 hours.
2. After selling, you use your voting power to change the settlement offset, depriving bitCNY owners of 5% of their holdings.

But we've had that discussion before, and I guess neither one of us will change their position.

Instead we should try to find a fair solution.

The real problem is a disparity of markets. You are quoting an outside market (magicwallet), which pays more than 1 CNY for a bitCNY. On the DEX, we see (right now) a trading price of 1.76 BTS/bitCNY and a feed price of 1.84 BTS/CNY, from which we can calculate that on the DEX you can buy at .956 CNY/bitCNY.

In order to realign the markets, trading must occur.
For example, someone could buy cheap bitCNY on the DEX and sell it on magicwallet for a profit. Or (which is what shorters should be doing), buy cheap bitCNY on the DEX, and close their position with a profit while at the same time pushing the DEX price up towards the feed price.

Why is that not happening?

according to your logic, now I should sell BTS in DEX to lower the price as feeded?

the problem is:
1. after I doing this, I have no way to buy BTS back at the feeded price, I am at risk if the BTS price goes up.
2. as a big shorter it's not easy to avoid being settlement by reducing debt,  even I avoid, some other shorters will be settled, as committee we need to find a solution to make sure any shorters won't be settled unfairly!

You don't have to buy BTS back, you can reduce your collateral as well as your debt.

listen, there is no low or high bitCNY price, bitCNY price are stable, there's only high or low BTS price,

That doesn't even make sense. Prices are always relative to something. The price of bitassets is expected to be unstable, because there is no fixed peg - it's a Market-Pegged Asset, and the market needs some space to move. The mechanism of MPAs encourages trading that moves the price towards the peg, that's how it works. This trading is currently not happening, which is at least partially responsible for both the market disparity and the current "speculators" who buy cheap and force-settle.

http://docs.bitshares.eu/_downloads/bitshares-financial-platform.pdf - section 2.

Great move!