I've created a graticule shapefile in QGis with extents [-180, 180, -80, 80] and step 20x10 degrees.
This is how it looks in QGis with and without re-projection.


(To be clear, I create graticule shapefile like this: in QGis Vector -> Research Tools -> Create Grid, using the extent parameters above, and then Vector -> Geometry Tools -> Densify By Count [180 points] to make latitude circles bend properly when reprojected)

When opened in SharpMap and then rendered on top of the map, the boundary latitude circle (80°) and longitude line (180°) is not rendered.

The boundary latitude circle is never rendered regardless of the shapefile extents I'm using when creating the graticule shapefile. 180° longitude line may sometimes be rendered - sometimes it depends on the Central Meridian parameter I use in my projection (there is actually quite strange behavior, like: when the parameter is 0° the line not rendered, when e.g. it is 90-94° the line is rendered, when it is 95-100° it is not rendered or may even be drawn diagonally across the map, when 101°+ - rendered fine).
Why could this be? Thanks in advance.