Make no mistake, investors didn’t need any more reasons to be bearish on Chinese equities.

Mainland markets are veritable casinos dominated by retail investors who until last summer, were enthralled with the prospect of easy riches in an environment where shares only seemed to know one direction: up.

All of that changed last June when a dramatic unwind in the half dozen backdoor margin lending channels that helped to fuel the rally triggered an epic rout that became self-fulfilling once the retail crowd (which accounts for 80% of the market) became rip sellers rather than dip buyers.

Since then, successive efforts on the part of the CSRC to stabilize the situation by pouring CNY1.5 trillion into A-shares has met with limited success as periods of calm are interrupted by violent bouts of selling like those we saw earlier this month when China tried and failed to implement a circuit breaker.

Throw in the ongoing yuan deval fiasco and there’s every reason not to be involved in Chinese stocks.

But when it rains it pours, and now, analysts say margin calls on SCLs are the next landmine that may pose a “systemic risk” for China’s battered markets.

“Some companies that had pledged shares as collateral for loans are now faced with a stark choice - dump them under pressure from impatient brokers and banks and book a loss, or stump up fresh cash or other assets to make up for the difference in value,” Reuters writes.

This is a rather large problem. Over half of all listed companies have their shares pledged. As BofA notes, “1,411 A-share companies have had some of their shares been pledged for SCLs by their major shareholders, representing 50.2% of the total number of A-shares. The value of stocks pledged for SCLs has been rising consistently - from Rmb2.36tr on 1 July 2015 to Rmb3.05tr by 1 Jan 2016, i.e., up by 29% in 2H15.”

In short, the steep decline in margin financing paints an incomplete picture when it comes to understanding how much leverage is in the system.

On one hand, the headline figure on margin financing suggests quite a bit of deleveraging has taken place since things hit peak absurdity last spring. Here's a look at how quickly the unwind materialized once things began to get dicey:

But as the SCL chart shown above demonstrates, the decline in headline margin debt only tells part of the story. Indeed, BofA says even the CNY3.05 trillion number for SCLs may be underestimate the amount of leverage in the market. "Our SCL data might have under-estimated the true extent of such activities because 1) only major shareholders, i.e., those who own more than 5% of a company’s stocks, are obliged to disclose their SCL activities; and 2) we have assumed a 12-month duration for the 2,889 deals, 44% of the total, that have no ending date disclosed vs. over 16 months on average for those that have," the bank writes.

Where things get truly frightening is when one looks under the hood on these deals.

Have a look at the following table which shows that of companies with pledged shares, an astonishing 82% were trading at a multiple of 50X or more at the time of their pledging:

"The collateral value," BofA says dryly, "is far from solid."

"If the market continues to fall, equity pledging-related selling pressure could increase significantly," Gao Ting, head of China strategy with UBS warns.

To let BofA tell it, fully a third of SCLs will face margin call pressure and some 371 of the 1,411 stocks pledged have already hit their triggers. "Assuming 40% loan-to-asset value at the time of SCL granting, our analysis suggests that by now, 371 stocks, worth Rmb641bn based on their current market values, have seen their share prices reached the stop-loss levels; and additional 281 stocks, worth Rmb310bn, the warning levels."

What happens when the margin calls start you ask? Well, nothing good.

"When a position has to be closed for transactions using floating shares as collateral, the pledger sells on the secondary market, putting further pressure on the stock market," Ting cautions.

Right. Which means stocks fall further and trigger more margin calls which means more forced liquidations in a never-ending, self reinforcing loop. Or, as Reuters puts it: "[It's] a vicious cycle where further share price drops are likely to trigger more margin calls and threaten further forced sales."

And this isn't some hypothetical - it's already started. "On Jan 18, some stocks of a company used as collaterals for a SCL were liquidated by the lender, which prompted its share price to limit down the next day," BofA recounts. "The stock had been suspended from trading since then. So far, at least 11 A-shares have been suspended as their prices approached the cut-loss levels."

"On Thursday, trading in shares of Maoye Communication and Network Co Ltd was halted after it said it received notice that its controlling shareholder faces margin calls, one of at least eight companies that have made similar announcements so far this year," Reuters adds.

Note that if this entire thing were to unwind it would be larger than if every bit of margin debt were squeezed out of the system. BofA figures the average loan-to-asset value is about 40%. Apply that to the CNY3.05 trillion pile of collateralized stocks and you've got the potential for a CNY1.22 trillion unwind.

And it gets still worse. Remember China's multi-trillion yuan black swan, the WMP industry? Well the WMPs are involved here too. Here's an example, again from BofA:

We cite a recently reported example involving the controlling shareholder of Guangxi Future Technology. According to articles by Securities Times (Jan 19) and 21st Century Business Herald (Jan 20), in December 2015 Pudong Development Bank set up a WMP called Tebon Huijin No.1 Asset Management Plan to fund the shareholder's purchase of its own company's shares. Essentially, the WMP buyers, as the senior tranche investors, lent money for the shareholder to buy their own stock. Similar to other structured WMPs, this product has a stop-loss clause, and the company's share price dropped below the stop-loss level on Jan 18. As the controlling shareholder did not put up additional margin, Pudong Development Bank liquidated all stock in the plan (equivalent to 2.13% of the company's outstanding shares). This is the first case of forced liquidation by such products but in our view there could be additional cases given how sharply the market has declined in recent weeks.

In short, this is a house of cards built on a still enormous amount of leverage. At the risk of mixing metaphors, the problem here is that once the dominos start to fall, it will be impossible to stop the downward momentum.

The takeaway: "we're going to need a bigger plunge protection team"...