Noticed this when trying out the Malian trade,
if you make the Landmark Tollpost or any other regular tollpost to close to either the Home market or Trade-post. They will generate a Toll revenue of +0food and +0gold.
My suspicion is this happens because they trigger on the Trader not having a set value on the very second it is created / value reset when trader touches the market/tradepost.
So you have to put a Tollpost at the minimum of 0.5 seconds away from the Market for it to trigger the Toll revenue propertly.