Undo & Redo in Word won't work

It is not that the short-cuts don’t work, it is the function of the undo/redu buttons itself that is not working. When looking at the downpointing arrow beside these button I can see whole list of edits made by EndnoteX associated with merey inserting one citation. When I try to undo each one of them, eventually something else written is changed without me being able to control it. Then it is impossible, for some uneqxplained reason, to undo those later edits in the order they were done. I have no problem with the short-cut per se, but with the function of undoing or redoing which are currently completely useless. This cannot be intended, right?