Postgresql 8.0 RC1 not using indexes

Hi,
I just installed 8.0 RC1 and then restored my database which was working
perfectly on 7.4.5.
I have a function that imports rows from a comma seperated file and on
7.4.5 using this same function I could get around 1000 rows every 2.5
seconds, now with 8.0 RC1 this has gone way up and it seems to be
because it is not using the indexes defined on the table.
The reason I believe this is that as the progresses the size of the
table increases and the time for every 1000 rows grows.
by the time I am up to 20000 rows it is taking over 30 seconds per 1000
rows.
I commit the transaction after every 1000 and on 7.4.5 there were no
issues.

The function in question does some selects on the table that is being
inserted and without the indexes working it ends up taking a very long time.

unfortunatly I can't supppy any of the plpgsql function code.