ya chummer 5 does this as well
if you have a magic 5/ess 6 character and put in a datajack, the magic does not go down, but the essence does. however, once you go past your magic rating in essence it drops 1 also.
altho, i think that may have been fixed?
EDIT:
just checked, the MAX magic rating does go down once you add the datajack. but the magic rating stays at its listing (unless you start with 6 magic) once you add another piece or pieces of ware that drops your essence past your magic rating then the attribute starts reflecting correctly