OK. Normally I’d suspect this to be the result of a conflict with your theme or another plugin but I see you indicated having already completed our standard troubleshooting steps:
YES, I’ve deactivated all other plugins to check for a plugin conflict.
YES, I’ve reverted to the 2011 default WordPress theme (with other plugins still deactivated) to check for a theme conflict.
Just for the avoidance of any doubt, can you confirm that you did indeed see no difference with regards to the featured image metabox after running through those steps?