I think that what Ishe might be confused about is a possible requirement to switch from HEADING mode (magnetically corrected heading) to TRACK mode (referenced to true north) when above a certain latitude.
I suspect this is a result of the magnetic variation lookup table not being available (not populated with variation data) above a certain latitude (probably about 80 degrees north), and also not being populated with magnetic variation data in the areas directly above the two magnetic poles.