I believe the bug is related to the trader's presence in the system...if they are not in the system when you drop the lane, their game will think it is still up. We used to encounter this problem quite a bit while pirating in Stuttgart (trigger happy people, I tell ya...).
But only dropping the lane when you get a contact is the best way to go about it, anyways...unless that contact is BHG|, [LN], LPI-, LNS, BAF|, BPA|, HMS, [KNF], KSP-, [RM], RFP| or RNC tagged... (you'd be surprised by the number of people that fail to cancel the lane next to the pirates, giving you precious seconds to turn round and press F2).
On the subject of pressing F2, always keep an eye on your getaway routes. Set waypoints on your preferred route so that, when said evil lawman comes along to spoil your fun (we was only playing football, honest...with big ships...), you can do a target/F2 to run like pussies =]