Is this a bug?

This is roughly the procedure I took:

1: create a brand name database.

2: create table(s) with psql utility.

3: connect to it using libpq, and do an insert at the very first run.

And the backend returns the infamous "transaction abored, query ignored"
message. However all the following inserts/deletes/updates worked.

But if I do this instead:

3: connect to it using libpq, and do a select call then an insert.

It then went through successfully. (Both the selection and insertion).

Was this a known issue on 7.2 or is it just something on my end I did wrong?

Thanks

Wei