Yep, that's what it is. Unfortunately, nothing I can do to fix this. The reason why is that in 3.161 (or thereabouts) the logic was wrong, which was causing extra harvesters in savegames from before that. Then, in 3.163, I fixed that back so that all the savegames from before were correct again, but now anything started in 3.161 (or which was relying on the wrong harvester positions in that, even if the save was older) will now be wrong, as here.
Clear as mud, no? But the bottom line is that you're a victim of a bug being fixed, but it's a very localized thing to a very specific set of savegames. It shouldn't make a huge difference overall, if you're really worried about it I'd suggest just deleting all your harvesters and letting them recreate themselves, they will then be right.
Sorry for the confusion! Hope that makes sense.