My experience of this is that is because Cura over extrudes the walls deliberately to help adhesion and strength - I want to say the setting is called “overlap”. It’s the one where the infil runs into the walls a little bit to tie together the edges, but that’s always going to result in a bit more plastic being laid down in those areas.

Normally it causes a bit of a brim to cut off, but in your case it might just be enough to let it stick round the brim but nowhere else.