Browsing through that thread I can see that I have similar symptoms:
$ pg_controldata | grep Multi
Latest checkpoint's NextMultiXactId: 1
Latest checkpoint's NextMultiOffset: 0
$ ls -l $PGDATA/pg_multixact/members
total 8
-rw------- 1 postgres dba 8192 May 3 08:21 0000
$ ls -l $PGDATA/pg_multixact/offsets
total 8
-rw------- 1 postgres dba 8192 May 3 08:49 0000
I don't see any resolution to that thread though.
Regards
Mikko