file_entity_edit_validate not executing: "Replace file" broken

I am working with a site that has the 7.x-2.0-alpha3 versions of Media and File Entity installed, and there seems to be a conflict with some other module that is causing the file_entity_edit_validate() function not to fire when editing an existing file. The tipoff was that the form was submitting without error, but the file would not actually be updated. Using a debugger, I was able to determine that the validate function was never actually executing.

When I add the validate function explicitly, like this, everything works great:

  $form['actions']['submit'] = array(
    '#type' => 'submit',
    '#value' => t('Save'),
    '#weight' => 5,
    '#submit' => array('file_entity_edit_submit'),
    '#validate' => array('file_entity_edit_validate'),
  );

This problem does not occur when installing a clean site from the same codebase, and just enabling Media and File Entity, so the problem definitely seems to be coming from an interaction with another module (of which there are many). Any idea where to start looking for something that could be conflicting with that validate function executing on the basis of the name alone?

Thanks for any help you can offer!