FMP 7 IWP bug: lookups of validated fields

I have a database configured for IWP. The main layout is supposed to work as a web form. The user creates a new record, then asks for a registration number, then there is a button to a script that does lookups of several fields in a related database, with the relationship based on the registration number. This way a registered user gets all his personal info entered into the new record he just created, and can then go on to fill in the information I need from them. This works well, until I attach a "Not Empty" validation to any of the fields in the main database. When I hit the lookup button the screen refreshes, but no lookups take place. This makes it impossible to force the user to enter data into all the required fields. Surely a bug?? What would be a workaround to force them to enter data into all fields?