coreutils       8.13-3.2ubuntu2 (quantal)

using the attached files:
$  LC_ALL=C sort rqb.2012-11-07. >/tmp/pC   #ensure inputs are sorted
$  LC_ALL=C sort a0>/tmp/qC
$  LC_ALL=C comm -2 /tmp/[pq]C>/tmp/-2
$  LC_ALL=C comm -23 /tmp/[pq]C>/tmp/-23

the 2 comm commands produce identical output!
oughtn't the latter command only show lines unique to FILE1?