My site uses both Magic Fields and Post Type Switcher. I noticed Magic Fields stopped updating posts, and to troubleshoot, I even tried downgrading to many older versions of Magic Fields.
The final solution for me was to Network Deactivate (I'm running Multisite) the plugin Post Type Switcher. To find that, I first disabled all my plugins, and when that didn't solve it, I went through and Network Deactivated all the rest of the plugins.
NOTE: Post Type Switcher is still active on the website, but when I 'Network Activate' it, Magic Fields stops updating my posts.