I'm pretty sure it was because of the Saif film with Dinesh Vijan. She was already shooting Kill Dil when Piku was offered to her. Even if the Ranbir film was true, he wouldn't have had started till this year (he hasn't even started ADHM or Ayaan's film yet) so she would have had time for Piku. She was supposed to start the Saif film mid last year, but it got delayed because Saif wanted to finish Phantom and focus on Happy Endings release. After Happy Endings flopped, the film got shelved.
I guess for Parineeti doing a film with Saif was a big deal as she used to have a crush on him. She once said she would even be happy working as a tree in his film.
This was in June last year:
Confesses Parineeti, "I've been a Saif Ali Khan fan for years. He makes me go weak in the knees." Talking about the film, Parineeti says, "Yes, I'm doing a film with Saif. Even as I say it I find it hard to believe. It will be produced by Saif's production house Illuminati. What is most interesting is that Saif's partner Dinesh Vijan will turn director with the film starring Saif and me. So I've double reason to be happy and excited." - See more at: http://indianexpress.com/article/entertainment/bollywood/parineeti-chopra-excited-about-working-with-her-crush-saif-ali-khan/#sthash.5AE12nP6.dpuf
Then this was in September:
She said, "My film with Saif Ali Khan is put on hold this year. The film was earlier scheduled to go sometime this year but now it has gone ahead because Saif is doing Reema's film first after
Phantom. I have to finish
Kill Dils promotions which will take almost the whole of November. This year we are not shooting this film, we will begin January onwards. Dinu is extremely busy with
Happy Endings. All three of us were busy so we decided to finish our respective work and come back for this project."
http://m.koimoi.com/bollywood-news/film-with-saif-will-go-on-floors-in-january-parineeti-chopra
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