It is exactly 10 years since the collapse of blue-chip US investment bank Lehman Brothers upended the financial system and brought the global economy to its knees.

Looking at markets now, I wonder whether one can look back on that crisis fully satisfied that history won't repeat itself, even though the financial system, at least measured by bank capitalization and the ability to withstand another meltdown, is in far better structural shape than it was a decade ago.

We know that the medicine used to fix the aftershocks - ultra low interest rates and quantitative easing in the US, Eurozone and Japan, plus a massive fiscal stimulus in China - helped avert a cataclysmic depression.

But we also know that the medicine created unwanted ills, in the form of ballooning debt - global debt stands at around US$250 trillion, or around two and a half times the debt mountain in 2008 - and the rise of a dangerous populism which has yet to play out to its full ramifications.

What the events of 2008 did show was that a market aberration, sometimes referred to as a "Black Swan" event, can prompt a domino effect and that contagion from seemingly unconnected markets can spread with precipitous swiftness.

In 2008 it started with the drying up of the asset-backed commercial paper (ABCP) market and the sudden loss of confidence in the short-term money markets, infamously characterized by the trading of the US$65 billion primary fund below a dollar.

The "breaking of the buck" on that fund came to symbolize the extreme stress underpinning markets at the time. All was not right. One wonders if things are all right at the current juncture in markets.

Emerging market sentiment has been soured by the turn in the US interest cycle, although perhaps tellingly, the emergence of a full-blown bear market in US Treasury bonds has yet to materialize, and the 10-year bond yield remains below 3%.

The collapse of the Turkish lira and Argentinean peso might be regarded in some quarters as idiosyncratic phenomena, but in fact they are symptomatic of the vulnerability of markets to excessive speculative forces, spurred on by algorithmic trading, lightning fast trade execution and the availability of cheap leverage.

A black swan-type event to exemplify a sense that things are not quite right is the huge loss suffered by private Norwegian investor Einar Aas last week on speculative positions in the European power markets. The 100 million euro loss he sustained blew through a ream of safeguards at a Nasdaq clearing house as he failed to meet margin calls.

These developments are not much when taken in isolation, but perhaps the start of a perception that extreme imbalance is accumulating in the market's psyche. The same is true for what happened with the Indonesian rupiah, which has crashed to levels not seen since the Asian Financial Crisis 20 years ago.

The explanation is that in the wake of the price action surrounding the lira and peso, foreign exchange market speculation has moved to punish the currency of any country that runs a current account deficit, as does Indonesia. The Indian rupee has been hammered for the same reason.

All it will take is the sudden dawning of the dangers of debt accumulation in emerging markets, accentuated by sharply devalued currencies, to shine a spotlight on that US$250 trillion global debt pile.

An undercapitalized IMF doesn't help proceedings if an EM currency rout unfolds precipitously, nor does the limited firepower available to central banks in an ultra-low interest rate environment.

One gets the sense that a dangerous October beckons as the 10th anniversary of the emergence of the full force of the crisis looms.