Have you tried:
- Editing the content class with the missing input fields ?
- Editing an existing version ? - Enable debug output and see if there are any error messages ?
OK, so I disabled Translation, but that didn't fix it. Then I clicked "Clear all Caches" in the debug section, and all of a sudden my input fields were back.
I'd clicked "Clear All Caches" in the Setup page of the Admin panel till I was blue in the face, and that didn't work. But clicking "Clear All Caches" in the debug section fixed it, apparently.