I am using Natural Earth coastline polygon (NE_10m_land), loaded from a shapefile in QGIS. All displays well (in, e.g., unprojected WGS84, EPSG 4326) - see below:
But when visualising in a polar projection (here, EPSG:3571, WGS84 in a North Pole LAEA Bering Sea projection), QGIS seems to lose the ability to distinguish between the inside and outside of polygons.
This does not seem to be a problem with the shapefile ( not well formed polygons) as I can visualize it using ArcGIS just fine.
Edit: It appears that it is indeed caused by Antarctica. Manual removal of Souther Hemisphere helps.