Specifically, in level 3, when you have to spin-jump onto the buzz saw here :

in ZSNES you are able to use the joypad D-pad keys to move left or right while you're auto-spin-jumping off of the saw but in Snex9x once you spin-jump onto the saw you get "stuck" and slowly drift left or right until you're dead -- pressing left or right doesn't work.
For example, take this video made with ZSNES :
http://www.youtube.com/watch?v=AhaiTc0Nlsk#t=4m17s
If someone can tell me how to create a video and load a save state after the video starts in Snes9x then I can post my version as well.
Regards,
jdb2