Currently Location addon works the following logic:
The selected location filters the employees. However, it does not work the other way round. If the employee is selected, the locations are not filtered. In practice this means that by selecting an employee, ALL of the possible locations appear in the dropdown.
When a location is selected that is not assigned to the selected employee, the system freezes and only a page refresh can solve this issue.
Please make it possible that the employee should filter the location, not only the location filters the employee.