As the tooltip of the "dismiss pheromone marker" states, clicking RMB on the marker should remove it, but currently, the player sets another marker by it.
It is impossible to remove the marker by clicking on the marker (the shape) or selected tile (check it by RMButtoning on the same space twice and fast).
It is impossible to remove the marker by clicking on the marker (the shape) or selected tile (check it by RMButtoning on the same space twice and fast).