It seems pretty clear to me, at least, that someone sent addresses of
the form "user @ node", which is not the same as "user@node", nor is it
the same as "user at node".  (I guess it's sort of exactly the opposite
of "useratnode"?).  I don't know RFC's enough to know if that's supposed
to be legal syntax or not, but that's my guess as to what's happening.
LISTSERV (or whomever) is checking the first whole word for a "@" and
not finding it because the "@" is the second word, all by itself.
Don't ask my how the process came up with the "@ WISCVM.WISC.EDU" as
someone's name- I'd imagine a name like that would have to be in
quotes in the first place to be a name, just as it was placed in quotes
when it was "preserved" as a name.  (And I would be astonished to find
that it came out as <IBM-NETS%BITNIC.BITNET "@ WISCVM.WISC.EDU">.)
 
Oh, such pleasant chaos!