Employee added to system multiple times

We have a custom form based off of HR11 that allows store managers to hire applicants into Lawson. Occaisionally we're seeing employee's being added multiple times (with contiguous employee numbers) to the employee table. Under normal circumstances HR11 will warn you when adding the same FICA number to the system, but it seems that this business logic is suppressed when the custom form runs and our form does not allow a duplicate FICA number to be hired so it sounds like the browser session is getting stuck and stacking the transactions. Has anyone ever run into anything like this?