BUGS

- When rendering on the command line using a cluster,
  it won't wait for pending histogram merges to arrive
  before terminating. On most cluster renders this isn't
  noticeable, but on very short renders of relatively large
  or oversampled images, the render can terminate while
  partial buffers have been merged, leaving ugly horizontal
  banding on the resulting image.

- When changing the size of the image, if a scrollbar is no
  longer needed it can end up as an artifact on the image
  drawing area.