Animated GIF is distorted when encoding from transparent GIF frames with ProgressiveEncoding enabled

I am creating an Animated GIF image from a set of transparent GIF image frames. The ImageWriteParam used in the writing process is set with ProgressiveMode - MODE_DEFAULT. When I read back the image using Toolkit APIs and render it, the output animated image is distorted. The quality of animation is very poor. This distortion is not seen when encoding the animated image with progressive encoding set to MODE_DISABLED. This distortion is not seen for non-transparent gif images. Creation of transparent animated GIF images is quite common and progressive encoding is enabled by default for GIF Writer.

This is reproducible on all platforms with Mustang-b43.

I have attached a sample test alongwith the image frames. Execute the sample test as follows.
'java WriterTest GIF' where GIF is the folder containing all the image frames. A frame will be shown with all the independent image frames and 2 animated images at the ned. If the last animated image is distorted, the bug is reproduced. Out of the last 2 animated images, first one is using MODE_DISABLED and second one is using MODE_DEFAULT. The second animated image will be distorted.