unexpected "ERROR: concurrent delete in progress"

While tracking down some issues that /might/ be kernel related, I ran
into an error message:

ERROR: concurrent delete in progress

With this SQL in a file (t.sql):

begin;
create temporary table foo as select x as a, ARRAY[x] as b FROM
generate_series(1, 10000000 ) AS x;
create index foo_a_idx on foo (a);
create index foo_b_idx on foo USING GIN (b);
rollback;

I had issued this bash:

while true; do psql -f t.sql test >> out 2>&1; done

and after a dozen or so iterations I encountered that error message.
Now, it *might* be kernel related, but what else might it be?
I'm on Linux x86_64, using postgresql 8.4.5.

--
Jon