Contact changes revert across Apple devices

Darnest thing. When I make a change to contact from let's say, my iPhone and go to my MacBook and make another change to that contact, it reverts back to what I entered on the iPhone. I've seen this on my MacBook, iPad and iPhone. The only way to make the new change permanent is to open a browser and go to iCloud. Is there a setting I am missing that allows contacts to be multi-user with file locking? Which device should be the master?

[Re-Titled by Moderator]

Original Title: Contact changes revert back