Well, it happened twice in my case. First, when I submitted additional docs (my travel history) upon their request. Then when I got PPR it again changed to "we need additional documents....". When I submitted my passports it again went back to "not needed".Thanks for the feedback and congrats on your PPR!
Can I ask, at what point/date did your doc status change to "not needed"?
Was it long before IP2 and PPR?