Magnetic coordinates and lines drawing across the world map

I'm extending basemap to work with magnetic coordinates. Basically, latitude longitude are converted to/from magnetic coordinates during calls to Basemap.__call__(). However, I get results like this:

It seems that coastlines/polygons are not properly "broken" on the left/right plot edges. I suspect I have to change something in _readboundarydata() to fix this (since that's where the coastlines and polygons are initiated), and I have had a look at it, but I do not really see what I would need to change. I don't even see how this is handled in the normal (geographic coordinates) case. There are some references to the crossing of east/west datelines, are these "datelines" the left/right map boundaries in projections like the above? I don't really understand what this part of the code accomplishes.

Any tips?

Comienza reproduciendo el mapa de coordenadas magnéticas mostrado en figure_1 y sigue cómo Basemap.call() transforma las coordenadas antes de que _readboundarydata() cree las líneas de costa y los polígonos. Lee la lógica existente para el cruce de la línea internacional de cambio de fecha hacia el este/oeste para determinar cómo se relaciona con los límites de la proyección. La tarea estará terminada cuando las líneas de costa y los polígonos se dividan correctamente en los bordes izquierdo y derecho del gráfico para las coordenadas magnéticas.