I was connected to the websockets API and watched this happen again:
getting mtgox depth
{"asks":[[1.6799,2],[1.68,100],[1.6899,9],[1.69,517.76],[1.69439,3.67],[1.69824,14.076],[1.70073,4.824],[1.70266,3.303],[1.799,37.52],[1.8,2.5],[1.85,3.78],[1.89999,9],[1.95,23.05],[1.9524,4.77],[1.9599,3.01],[1.97,9],[1.9791,504.21],[1.98,32],[1.98699,450],[1.987,86.21],[1.988,9.94],[1.9884,50],[1.9885,50],[1.9889,333],[1.9999,32.27],[2,9175.02],[2.2,1312],[2.4,1000],[2.4056,49.68],[2.48,700],[2.4999,600],[2.5,87.98],[2.6,1000],[2.65,50],[2.71,544],[2.72,500],[2.74568,10]],"bids":[[1.6303,300],[1.6301,1.5],[1.63,91],[1.6201,2],[1.62,1000],[1.61395,1.066],[1.612,100],[1.6,172.923],[1.5999,4.96],[1.59,10],[1.589,10],[1.5889,1.98],[1.583,5],[1.5829,3.36],[1.58,91.39],[1.5799,7],[1.579,10],[1.575,13.644],[1.5749,9],[1.57,1009.76],[1.5688,20],[1.54,533.455],[1.52,1000],[1.51,5.26],[1.5003,1],[1.5002,20],[1.5,20],[1.4835,50],[1.4834,50],[1.4833,50],[1.4831,104.268],[1.483,48],[1.4807,9.111],[1.4805,3.55],[1.472,2.634],[1.47,1020.068],[1.46511,102],[1.4606,101],[1.4335,27.555],[1.42,1000],[1.401,25],[1.4001,1000],[1.4,60],[1.39,10],[1.385,2.5],[1.372,35],[1.3675,50.1],[1.36,100],[1.3559,100],[1.352,200],[1.35,35],[1.341,51.06],[1.34,151.537],[1.3301,99.141],[1.33,7100],[1.32011,12.869],[1.32,5],[1.31,10],[1.301,500],[1.3,406.58],[1.295,100],[1.291,42],[1.2903,199.14],[1.2901,54.22],[1.29,122],[1.26,1],[1.2581,2],[1.254,7.743],[1.2502,3.551],[1.25,821],[1.21,75.454],[1.2022,52],[1.2011,54.329],[1.201,503.271],[1.2,2125.925],[1.19,16.75],[1.18,1],[1.175,6]]}
MessageEvent
{"channel":"dbf1dee9-4f2e-4a08-8cb7-748919a71b21","op":"private","origin":"broadcast","private":"trade","trade":{"amount":511.214,"date":1303606410,"price":1.6,"tid":"45433","type":"trade"}}
After reading [https://mtgox.com/support/darkPool], if a normal sell order is placed that can partially fill a dark pool buy order, it should fill the higher priced normal bids before partially filling a dark order. Unless I'm mistaken, it doesn't look that happened here.
Dark pool Only - Can be filled only by other dark pool orders or a single normal order that is larger than the dark pool order. This means that if there is a single normal order that would fill the dark pool order both will be filled.
I read that as a dark pool order can only be filled by other dark orders or a single normal order. This situation could happen if there was an existing ask of 1.6 that is greater than 1000 (since that's the largest bid 1.6 or above). With that ask in place and the order book you showed, a dark order bid for
[email protected] would be filled from that ask.