I think this is a bug.
When creating review, if I choose someone else for moderator, I still see Start Review button. When I hit that, I get an error You are not authorized to make the requested state change.
If I click Done on that popup, it closes fine, and still have a Start Review button at the top.
If I refresh page, Start Review button becomes Send To Moderator and that is what it should be.
This occurs when using the default permission scheme. When you change the moderator, the page is not reloaded to refect the change in the available action from "Start Review" to "Send To Moderator".
This is a bug and there is an issue for this: https://jira.atlassian.com/browse/CRUC-1957