With GCKI and Cargo Ships installed. Open personal logistic requests, and you see two items, "indep-boat" and "GCKI-dummy-item_indep-boat". What is the dummy item for? Should it be visible?

I also found that normal boat and indep-boat are both visible, which I will need to fix on my end.

With GCKI and Cargo Ships installed. Open personal logistic requests, and you see two items, "indep-boat" and "GCKI-dummy-item_indep-boat".

Thanks for the report, I'll look into it.

What is the dummy item for? Should it be visible?

See data-final-fixes.lua:

-- "DMV Directional Movement Vehicles" will create a spider-vehicle for each car
-- prototype and overwrite the place_result of the car item. We must create a new
-- item that will place the original prototype so that we can get the vehicle icon
-- for use in our GUIs (If DMV is added to a running game, car-based entities that
-- already are used in the game would have no icon on the GUI.)
GCKI.writeDebug("data-final-fixes.lua: Recreate items for car prototypes?")
require("prototypes.3-recreate-car-items")

I also found that normal boat and indep-boat are both visible, which I will need to fix on my end.

OK.

Unfortunately, I can't test right now because I'm syncing a saved file to reproduce a bug, and there are >150 mods to download, so that may take some time …

I guess this would be fixed by adding new_item.flags = {"hidden"} before extending the new item's data in prototypes.3-recreate-car-items:

if to_place ~= placed_by then
      new_item = table.deepcopy(items[placed_by])
      new_item.name = "GCKI-dummy-item_"..new_item.name
      new_item.place_result = car.name
      data:extend({new_item})
      GCKI.created_msg(new_item)

Should be fixed in version 1.1.5.