I have had similar issues with NAB over the years - an order on an illiquid stock that hasn't traded for hours triggering a line-wipe on the stock in question. Both when my order transits directly to market and when it is held up 'for inspection'. NAB deny this has anything to do with them, but for it to be pure chance? It has happened too often and on thinly traded stocks from my experience.
Worst are when NAB prevents you from placing an order at the very next price level (say 0.5c increment) and then someone line wipes it while the order is being 'assessed'.
I guess possibilities might be an order inspector trading on the side or a third party has been able to compromise the NAB/AIEX order entry with a HFT bot?
Anyway, I didn't like the 'coincidences' so most of my trading is done on WebIress now.
