Uploading an image in the edit cell overlay after deleting the existing fails

Steps:
- double click cell with a poster image, edit cell overlay opens
- delete image clicking the "x" in the preview
- upload new image using button below preview
  (- broken image icon appears after upload)
- click save, cell shows no image (greenish with X)
- open edit overlay again, no image there
- upload again, save, now it works

Chrome 30.0.x on 10.8
