Odd plpgsql behaviour

On 7.4:

This is what we wanted to do:

IF TG_OP = 'INSERT' OR (TG_OP = 'UPDATE' AND NEW.name != OLD.name) THEN
EXECUTE x;
END IF;

However, we had to write it like this:

IF TG_OP = 'INSERT' THEN
EXECUTE x;
ELSIF TG_OP = 'UPDATE' AND NEW.name != OLD.name THEN
EXECUTE x;
END IF;

Because in the first case it would complain that OLD.name wasn't
defined, if the trigger was NOT an update.

OK, but the second case works??!?! Is this a weird peculiarity of the
pl/pgsql lazy evaluation rules? Why doesn't the first one work if the
second one does?

Chris