User blog comment:Kirkburn/Technical Update: August 12, 2014/@comment-452-20140812204807/@comment-452-20140813124410

That sounds like completely "standard" broken behaviour of images on Wikia to me. As always, all current uses of the image has not updated from anywhere from a few hours to a week, but if you post an image of a different size, that new thumb is generated from the new file.

But if clearing your browser cache fixes the issue, then the issue is clearly your browser, and not anything to do with Wikia.