i have seen a few that do this if they think you might drop
anchor where your swing maybe to close. i have seen more who do this if they think you might drop
anchor in the same zip code.
screw em, assume they have 3-5 to 1 scope, and you will have 7 to 1 , just make sure you are far enough away
if you do have to get close come up from behind, and either cross the stern, looking for a stern anchor or come along side from astern. that gives you the best ablity to turn away even if they swing suddenly