7.0.2 -> 7.1 performance drop

When I upgraded from 7.0.2 to 7.1, one of my batch scripts went from 10 to
20 minutes?

Some time ago I wrote a script that imports a 1.5M text file into 3 tables
(about 7K, 9K, 9.5K rows). I had set the script to run nightly when the
input file was changing regularly. However, the input hasn't changed now
for several weeks. Last week I upgraded from 7.0.2 to 7.1 and now notice
that the script takes 20min instead of 10min. I'm running on an OpenBSD
box and pg releases were installed from 2.8 and 2.9 packages respectively.
The OpenBSD upgrade is not a factor, because I upgraded that first and was
running 7.0.2 under 2.9 (script was still 10 min) for about three weeks
before the pg upgrade. The script just deletes all rows in tables, imports
data as seperate inserts for each row, then does vaccum analyse on the
tables. I've read that delete/rebuild of indexes will likely improve
performance of this script, but the runtime itself is not really a concern
here, just the change in runtime between releases. I'm curious what
changed between releases to cause the slower processing?

Frank