pg_dump, restore and versioning

I'm having a problem ever since restoring a database after a recent
server crash. Everytime I try restore the database from the dump file
the tuples are triplicated, that's including OID's. (If I "SELECT * FROM
mailing_list WHERE lastname like 'Somename';" I get three exact copies
of a record) This is not the result of a replication of values in the
dumpfile. I strongly suspect that the cause is because some editing was
done on the dumpfile in a Postgresql v7.1 db on another machine and the
server is running v6.5.

Are there any known issues with restoring dumpfiles from later versions
of Postgresql into earlier versions? If so - or if not for that matter -
is there any known way around this problem? Or is it time to upgrade?

kind regards,
sol