Hi Ben,
I have just tested it. When you enter a user into the search field all invoices will be filtered and compared to all users’ fields (Customer billing address fields). Only invoices that have all the same values (name, surname, company’s name) will be shown.
Please, check a user’s profile and see if you have not added additional information into that client’s profile (Customer billing address).
I will inform programmers to check that issue further (especially when dealing with empty fields of other users) so that the search results are properly filtered.
best regards,