I know for a fact that if you accept the common defaults (port=1521,etc.),
then no listener.ora file is required for a V10 instance.
I suggest that you rename all listener.ora file out of the way & try again.
IMO, it the V9 listener.log file is being updated, then the V9 listener is REALLY, REALLY the one being invoked.
HTH & YMMV!