J and M are next to each other on a QWERTY keyboard. I say typo.
Actually, although you are still quite smart for using Linux (Debian > * b***hes), it is not actually a typo.
You'll see this in other opinions as well (all that I've looked at, in fact) - both supreme court and COA.
I think the J just refers to the fact they are a justice or judge. I'm not 100% sure, but this is the only thing I can think of. You'll also see P.J. (I'm guessing Primary Justice/Judge) and JJ (probably just indicative of a 'regular' Justice/Judge).
So for example, if you look at the Partial Concurrence/Dissent (
http://publicdocs.courts.mi.gov:81/opinions/final/coa/20121025_c304582(65)_rptr_140o-304582-final.pdf) for the COA case, you'll see GLEICHER, P.J. even though the first name and middle initital are Elizabeth L.
Like I said, I'm not 100% what the J stands for, but I'm 99.999999999999999999999% that it's not a typo.