User blog comment:Kirkburn/Technical Update: December 2, 2015/@comment-24801399-20151203053212/@comment-126761-20151203141554

Indeed!

I should note: GIF resizing is a surprisingly complex thing to perfect. While this fix should solve a lot of the recent issues with thumbnails getting messed up, some may potentially still look odd.

If a newly generated GIF thumbnail continues to exhibit problems (a quick way of generating a new one is to resize the image by 1px), please do let us know via Special:Contact/bug!