title: ImageList#montage not including most photos
body: <p>I have this code:</p>
  
  <pre><code>marginsBetween = 20
  background = '#000000'
  
  columns = 6
  rows = 12
  
  collage = images.montage {
    self.geometry = '+' + (marginsBetween/2).to_s + '+' + (marginsBetween/2).to_s
    self.tile = columns.to_s + 'x' + rows.to_s
    self.background_color = background
  }
  </code></pre>
  
  <p><code>images</code> is an ImageList with 96 images in it, populated as follows</p>
  
  <pre><code>images = ImageList.new()
  urls.each do |url|
    images &lt;&lt; Image.read(url)[0]
  end
  </code></pre>
  
  <p>Where <code>urls</code> is just an array of image URLs</p>
  
  <p>For some reason, after calling <code>collage.flatten_image</code> and saving that resulting image, I only have 24 photos in the grid with whitespace filling the rest.  Has anyone seen this behavior before?</p>
  
  <p><strong>EDIT:</strong>
  It appears that this only happends with 96 images.... Any other number works fine</p>