Quote from Hoi:
Hi OldTrader (good you are posting again).
I can add some more info if you like.
IB's MarketDepth-feed is from the very start (summer 2003, or was it 2002?) wrongly designed and implemented (I know this, as at that time I have deciphered the protocol to the bit and bytes). It is built to transport extremely fast, only the changes in the Depth-book, but thereby lacks (and that is the design problem) a "verify-completion-correction-recover" protocol.
Until IB redesigns the whole MarketDepth transport protocol (inclusive error-recovery) we will see the problems stated in this Thread (and many other ET-threads and Forums).
Problems will show like the screenshot in this thread: the levels on both sides out-of-sync. Or it will show by wrongly sorted price-rows in one or both levels. Or there will be Gaps and standing still. This will be in the TWS-market-depth window, as well in the BookTrader, as well in all API-programs, simply because they all depend on the very same transport-protocol.
Hoi (designer of ButtonTrader).