"Export Folder" custom parameter still taken into account even if deactivated

Hello. In an export plugin, I am trying to deactivate the “Export Folder” custom parameter on exporting instances. This works, but the deactivated parameter is still used by Glyphs when exporting the instance.

Adding a print(instance.customParameters["Export Folder"]) correctly yields None, however, the instance is still exported into that folder.

I can’t reproduce this. Can you send me a sample file?