When the order is not fullfilled immediately, only one transfer to the market is done. In this case,
len(logs["events"]) == 1
and the order is added to the buyBook or sellBook. When then a new ordre is placed which is able to fullfill it, this new order has more than 1 entry in events.
So, not fullfilled order are build up and the token are locked into the marked. When there is a sucessfully buy/sell, tokens are moved out the market. The movements can be tracked by checking all entries in log["events"]