For me, the inputis not firing on mediumedtior in IE11.
According to this: https://connect.microsoft.com/IE/feedback/details/794285/ie10-11-input-event-does-not-fire-on-div-with-contenteditable-set, the input event doesn't fire on any contenteditables (not just mediumeditor) in IE10 or IE11:
I've confirmed this in my IE11 VM using the fiddle mentioned on the above page: http://jsfiddle.net/7VQxd/
But the ReadMe for this project says that the input event should work in IE9+. Anyone else having this issue?