When comparing frames in GifImagePlugin, use a frame unmodified by _get_palette_bytes

PIL/GifImagePlugin.py

@@ -365,6 +365,7 @@ def _save(im, fp, filename, save_all=False):
                 # e.g. getdata(im_frame, duration=1000)
                 if not previous:
                     # global header
+                    previous = im_frame.copy()
                     first_frame = getheader(im_frame, palette, encoderinfo)[0]
                     first_frame += getdata(im_frame, (0, 0), **encoderinfo)
                 else:
@@ -386,7 +387,7 @@ def _save(im, fp, filename, save_all=False):
                     else:
                         # FIXME: what should we do in this case?
                         pass
-                previous = im_frame
+                    previous = im_frame
         if first_frame:
             save_all = False
     if not save_all:

Tests/test_file_gif.py

@@ -406,10 +406,10 @@ class TestFileGif(PillowTestCase):
 
     def test_transparent_optimize(self):
         # from issue #2195, if the transparent color is incorrectly
-        # optimized out, gif loses transparency Need a palette that
-        # isn't using the 0 color, and one that's > 128 items where
-        # the transparent color is actually the top palette entry to
-        # trigger the bug.
+        # optimized out, gif loses transparency
+        # Need a palette that isn't using the 0 color, and one
+        # that's > 128 items where the transparent color is actually
+        # the top palette entry to trigger the bug.
 
         from PIL import ImagePalette
 
@@ -425,7 +425,17 @@ class TestFileGif(PillowTestCase):
         reloaded = Image.open(out)
 
         self.assertEqual(reloaded.info['transparency'], 253)
-        
+
+    def test_bbox(self):
+        out = self.tempfile('temp.gif')
+
+        im = Image.new('RGB', (100,100), '#fff')
+        ims = [Image.new("RGB", (100,100), '#000')]
+        im.save(out, save_all=True, append_images=ims)
+
+        reread = Image.open(out)
+        self.assertEqual(reread.n_frames, 2)
+
 
 if __name__ == '__main__':
     unittest.main()