Sorry, I don't understand why, but I've tried by removing, deleting, and uploading a picture and set it as a featured image so that it appears as a thumbnail any where that it has got to be one. But even though that there's an image / picture set as a featured image, it would uses nrelated 'defaulted' image as a replacement.
Please help. I wish I can attach picture here, but there's option for that sort of thing. Sorry.
http://www.posterkini.com/khabar-angin-pelacuran-pelakon-korea/ < this is the link to the story, that may or may not appear with your default image.