A few years ago I was working in a startup where the designer was given way too much decisional power (he was friends with the owner).

He had a tendency to keep editing parts of the design during the development phases, so when we had to work on a new big section of the application, before starting the tront-end development, I asked him to confirm that the mockups were final.

He confirmed the design was final and was not going to change.

10 days later, of couse, he sent a new, completely different, set of mockups. The startup owner expected the new design to be implemented without moving the deadline.

(I left that startup shortly after. The issues with the designer were just the tip of the iceberg.
The owner tried to keep a payment hostage to "force" me to sign a new 1 year contract. He backtracked when he thought I was recording the call. I got my payment and left.)