I have just been informed by IB support that they have resolved an issue I have been witnessing with the ASX exchange producing phantom prices under certain conditions. The release of the fix is tentatively on this Friday.
The fix applies to all combo-to-combo trades of ASX. ASX confirmed that the bad ticks were leg executions of a combo-to-combo trade. When a combo matches another combo, ASX uses a special formula to calculate the execution price, which maybe quite different from the outright execution prices. I have seen such calculated prices being displayed on TWS and MC in real-time and historical downloads that were way above the market ask or way below the market bid price. The forthcoming fix will exclude these prices.
I believe by enabling "Generate a new tick if Total Volume changes" MC can correct for such phantom prices as I've noticed the up+down volume is 0. However, this workaround only works for real-time data. The IB fix hopefully will correct this for historical downloads as well.