Yeah, I noticed this when I applied my maximum overscan mentioned in the overscan thread on my A600
According to HRM, 00 and ff should be valid DIWSTRT and DIWSTOP - it would be interesting to know if there's a HRM updated for ECS that mentions why ECS has this "limitation". 00 and ff works fine on OCS, which is what the HRM is written for, I guess. Until I see / hear otherwise
Maybe this nice thread will end up as a HRM addendum