It doesn’t bother me when they change their mind. What bothers me is when they refuse to document it. Every change should be documented. Print it out and get them to sign it. Then when they complain whip out your pile of documents and say, “Here’s where you asked for X, changed your mind to Y, then back to X, then something new to Z. Is that your signature?”

Devs are expected to have a ticket to track everything they do, so should the product managers. There should also be tickets for meetings so I can track how much time was subtracted from development by useless meetings.