Application diagnostics resposibility auto assign

[emm]

R12.0.6
db: 10.2.0.2.0.
I made a user which ranks high in the approval hierarchy

I assigned him Purchasing smart user responsibility with extra rights

I had been assigning this responsibility since 1 month now to high users

But since 2 days, i am noticing that when i go to Secutity>Users in system administration, in thier indirect responsibilities, "application diagnostics: is assigning automatically and the inactive date is also disabled

How am i supposed to deactivate and prevent it in future?