Hi Andrew,
you are right. This blue dot to mark the clipping can be confusing. If, however, you set the ClippingStyle to False, that problem can be solved, too:
ListLinePlot[{{{0, 400}, {10, 400}, {85, 335}, {400, 335}}, {{0, 650}, {10, 650}, {335, 400}, {400, 400}}, {{0, 400}, {8, 400}, {200, 260}, {400, 260}}}, PlotMarkers -> {Automatic}, ClippingStyle -> False]
Cheers,
Marco