pgdump problem or question?

Early Friday morning a bad record caused me to reload the Thursday night pgdump backup. I performed a pgdump first to study later. In the backup I found several incomplete transactions all done at the end of the day. Investigating later I found the original bad record from the Friday dump and fixed it then found that those incomplete transactions were complete in that version.

The client shuts the system down nightly by first closing the application then performing a pgdump on the database before shutting it down then shuts down the computer (Windows XP PRO, PostgreSQL 8.3.3). The pgdump would have taken place at least a couple of minutes after the application shutdown.

I thought pgdump was suitable for a live backup of the database. This would seem to be wrong if it dumps partial transactions. Do I understand correctly? If so, is there something else I need to do before the dump? Any help will be greatly appreciated. This does shake my confidence in my backup procedures.

Thanks,
Bayless