Property registration mumbai

I have a registered power of attorney given by my elder sister in my name for look after and sell out her residential flat at Virar, Mumbai. POA registered at Kolkata as she used to live here. Now concern person at Mumbai told me that registration of purchase documents I have to go through some adjudication of registered POA as the same is not registered at Mumbai (as suggested by registrar) and further it will take 3 to 4 business days. Being a practicing advocate I could not understand the whole process as per I know a registered POA is valid all over India and no need to further revalidation. As such kindly clarify. I am requesting those who specifically practicing at Mumbai and/or having knowledge over the rules and regulation. Thanking you anticipating an early cooperation in this regard.