Invest1 publisher3 min readPublished
Two stocks, PonyLink and Valofe, swung more than 32% in the four hours KRX added to the trading day
KRX scrapped 10-minute single-price matching for continuous trading between 4 p.m. and 8 p.m., and on the first day the biggest movers round-tripped, with Hanwha Galleria finishing about 0.9% below its regular-session close.
The Investor · Invest desk
What happened
- The Korea Exchange began running a 4 p.m. to 8 p.m. after-market session on Sept. 14 in which KOSPI and KOSDAQ stocks can be bought and sold in real time after the regular close.
- Several small- and mid-cap stocks swung sharply within minutes on the opening day, with volatility widening in names where trading volume and resting orders had not built up enough.
- Separately, Mirae Asset Securities customers trading the NXT pre-market had delays retrieving execution records between 8 a.m. and 8:50 a.m., and the broker rerouted orders to KRX to clear it.
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Why it matters
- constraint An order that would once have waited for the next 10-minute call now executes against whatever resting size is in the book. In a thin KOSDAQ name, the cost of immediacy falls on whoever crosses first.
- contradiction KRX blames thin early participation, which implies the swings shrink; its own session also lists far more stocks than NXT, and that breadth stays where the exchange set it as time passes.
- exposure Samsung Securities customers had pre-market orders execute after cancelling or amending them, and that liability sits with the broker's order systems, not with the exchange.
- decision Desks working size in Korean small caps now have to decide whether to trade the extra four hours at all, knowing a fill can be interrupted by a two-minute single-price auction.
Hanwha Galleria's 3,070 won high was 15.4% above the regular-session close [3], which puts that close near 2,660 won [1]. By about 7:50 p.m. the stock was 2,635 won [7], roughly 0.9% below where the day session had left it [2]. The 19.2% high-to-low gap [7] implies a low near 2,576 won [3], so the late print sat about 59 won above the session's worst level. Seoul Economic Daily reported the move came amid talk that Galleria Department Store's Time World branch in Daejeon could be sold. The paper cited retail industry officials saying the branch's management planning office recently briefed employees on the matter [4].
The KOSDAQ names did the same thing faster. PonyLink's 3,150 won high was 29.90% above its opening price [8], which implies an open near 2,425 won [4]. At 7:50 p.m. it traded at 2,435 won [11], about 0.4% above that open [5]. Valofe opened near 2,300 won [6] and was at 2,370 won by the same time [11], up roughly 3% [7]. The session ranges were 32.35% and 32.01% [8][9].
Continuous auction means an order executes the moment it matches [2]. Under the abolished design a marketable order waited for the next 10-minute call and took a single price alongside everyone else's [2]. What survives of that is the static volatility interruption, which switches a stock into a two-minute single-price auction when it moves beyond a set range from its reference price [6]. KRX triggered two on Hanwha Galleria, at 4:13 p.m. and 5:13 p.m. [5], so about four minutes of the 240-minute session ran as auctions [8].
The exchange's own explanation cuts against reading day one as permanent. KRX attributes the wider swings to a shortage of participants in the early days of the session, when even small orders move prices sharply [12]. If participation is the binding constraint, the tails narrow as volume arrives and the 32% ranges were a cold start. If coverage is the constraint, they do not. The KRX after-market lists far more stocks than rival NXT, and order-book gaps show up worst in thinly traded small caps [13]. I would expect the ranges to narrow without closing, since breadth of coverage is the exchange's fixed choice and participation is not. If the second week's small-cap high-low gaps come in near regular-session ranges, the cold-start reading wins and there is no new execution risk to price.
The day's operational failures were in the morning, on the other venue. At Mirae Asset Securities, some investors trading the NXT pre-market had delays retrieving execution records on the firm's home and mobile trading systems between 8 a.m. and 8:50 a.m. The broker rerouted smart order routing orders to KRX from 8:50 a.m., clearing the problem before the 9 a.m. open [14]. Samsung Securities reported pre-market orders executing after they had been cancelled or amended, and available order amounts showing zero for customers holding cash balances [15].
What to watch
- Second-week high-low ranges in PonyLink, Valofe and Hanwha Galleria: convergence toward regular-session ranges would settle whether day one was a cold start.
- Whether KRX narrows the after-market's stock coverage or adjusts static volatility interruption bands after the day-one interruptions.
- Whether Samsung Securities and Mirae Asset Securities report further order-system faults as extended-hours volume builds.