If you are using a lens wider than 35mm you have the following choices:
No IR filter, no code: your shots will suffer from IR contamination, blacks will be some degree of magenta and foliage will not be true, at the very least.
IR Filter, no code: You will have the cyan corners that Ben mentioned. This can be fixed in processing with Cornerfix or other software.
IR filter, coding, camera menu set to IR filter ON: The M8 will correct the corners for you.
This "coding" could be handled in a menu item, but Leica has chosen not to implement this capability.