ACE seems to exhibit the same issue as Leaflet/Leaflet#916.
That issue has already been fixed (with a one-line change!), so it should be fairly easy to patch ACE as well :)
cc @avih (you might want to include this info somewhere in the SmoothWheel docs?)
Thanks for the report. This is fixed now, but we might have to revert it if stopping the event interferes too much with other mousewheel event listeners on the page.
Thanks @nightwing! Please make a note here if a revert is made.