Quote from cashonly:
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I've seen it happen in a halted stock. For example, the NYSE halted the stock, and it took the ECN a minute or two to get around to halting it and the trader did a trade in the interim...
There's a problem that occurs with NYSE stocks, though, particularly during the pre- and post-market sessions. The problem is that the ECNs (at least Instinet) respect the halt time that NASDAQ dictates, not the one issued by the NYSE. This apparently occurs because the whole process is manual. The company calls the NYSE to halt the stock, they call downstairs to have it pulled from the crossing session, and someone then manually tells the NASDAQ about it. NASDAQ then issues their own halt. Meanwhile, the news may already have come out, and people get whacked on the ECNs, defeating the whole purpose of the halt.
This happened to me on January 22, with the after-market news from TXN. TXN called the NYSE around 16:29 (they don't record the seconds), at which point they pulled it. The first headline hit the wires (Reuters, in this case) at 16:30:29. NASDAQ didn't halt the stock until 16:30:40, 11 seconds later, during which time thousands of shares traded on Instinet (including me getting short 700 at what turned out to be about a buck too low :-(). NASDAQ refused to adjust their halt time, even given the timeline described above, and Instinet refused to honor the earlier NYSE halt, even though it was clear that they should have done so in order to ensure integrity of the market.
Of course, the primary problem is that TXN released their news such a short time after telling the NYSE, which wasn't enough time to get it halted everywhere. I wish the issuers would get this right, and that the NYSE would remind them about the necessary time frames.
Nobody would give a good reason for their decision, other than "it's policy", as usual. It's too bad that there is no immediate means of review of these types of bad decisions. The best you can do is complain to regulators, but this process takes so long, and so rarely produces any results, that most people (including me) don't bother - and the bad decisions just keep coming.
Writing about this has gotten me riled up about it again - maybe I'll go through the trouble to write to the parties involved.