Here's what Stephan Sbazo on pgsql-bugs had to say:
Wait, okay, I think I know what happened. There was a problem with 7.0.?
dumps not having the information about the "other" table in the references
constraint written out so when you dropped the table it didn't realize
it needed to drop the trigger. You may want to drop the constraint
triggers and recreate them with alter table add constraint.
(I'd created the table in 7.0.2 before upgrading.)
