Concurrent User issue

I have a very small (5 user) install. I am having an issue with these 5 people entering purchase invoices concurrently. If Person A starts the invoice, then doesn't immediately enter information, the invoice appears to be blank. It just has an invoice number with no additional information.

Person B can then enter information into that invoice. This causes problems. For one, it is not a good audit trail. Secondly, when Person A returns to their invoice (it still appears ready for entry on their screen) the get an error telling them that another user has modified the record.

Is there a way I can have multiple users enter invoices at the same time without running into this type of conflict? I'm sure a company with an AP department of 20 or 50 users doesn't deal with this kind of thing. It seems like this is a setup issue.

Thanks.