PPI on JI

Database
mjj
Teradata Employee

PPI on JI

Hi,
I have created JI on some tables. The largest table in base tables has PPI defined.
When i had fired a partially covered query, JI was used.

After that I have modified JI, created same PPI on JI and fired same query.
But this time it's not using JI.

Can anyone tell me why this is so?