Bug in contour plotting on 'cyl' basemap

When using an equidistant cylindrical projection over a selected subregion of the globe, e.g. map = Basemap(llcrnrlon=50,llcrnrlat=-80,urcrnrlon=300,urcrnrlat=70,projection=‘cyl’),
any contour plot that I try and generate (i.e. any plot generated using the map.contour() function) cannot plot any values south of 10N. In other words, everything south of 10N just shows up blank on the plot. It works fine for filled contours (i.e. map.contourf()), but not for simple contour lines (map.contour()).

Has anyone else come across this issue?