[onetwo_threefour]

Also, check your macros. We had this happen at work a couple of times and it turned out that word had been shutdown improperly and had created a macro that messed up the insert/replace function. If you use macros you should be able to recognise it because it will be one you didn't create and will have a weird name. I'd you don't use macros, it may be the only thing listed when you view macros. (and it will have an unusual name as well)