I upload a little test named "pb_ibo_2".

I use :

 - the employee.FDB database.

- a IBOQuery to show the EMPLOYEE table ("SELECT * FROM EMPLOYEE ORDER BY EMP_NO")

- A TRadioGroup to play with the Filter property on the PHONE_EXT Field.

1) Open the DB 

2) go to the employee #72 (phone_ext is null)

3) Enter "1" and press enter

4) Click on filter "phone_ext" is null

5) you show the #72 in the list with a value

I added a checkbox to open the database with or without the CachedUpdates enabled. When the CachedUpdates is disabled, the filter works.

Best regards,

Laurent.