Refreshing the page, even opening in a new tab, did nothing. Clearing a cache of 1GB solved the issue, but is this a known issue?
It is a problem with Chrome (and now Firefox, since they tend to copy Google's bad ideas)
Usually you can force refreshing the page without cache by pressing Ctrl+Shift+R or Ctrl+F5 (or Cmd instead of Ctrl on Mac, I assume)
About that pic replacement, when replacing a pic by a different one (different scene/episode) usually we keep the old pic in the comments (except if it really has no interest)