When I right-click the carbonite map, click MiniMap and check the full-size option it works for a while and then reverts to not being checked. I have tried everything I can think of to fix it.
Are you logging out and back in on the same or other character? That setting is not saved, so on log in it would be off. Leaving an instance may also be turning it off.
You can set a key a keybinding to toggle it quickly. I use 'I'.