1) Good, if it was intentional I'd have a lot of work to do!
2) Affected NPCW on classic: Leapfrog
3) The primary problem is that the Graphics Reviewers cannot view the MNGs generated by gif2mng with the plugin from
http://www.libmng.com/plugins/index.html , which is the only one I've been able to find for them...granted that Graal only supports a limited subset, but it seems to be a very rare subset!