I’m not sure how I do it, but from time to time pressing Shift + ? doesn’t give me ? but an accented capital E. My wife showed me how to turn it off with Shift + Ctrl + Shift (i.e., press all three keys at once [yes, both Shift keys]), but I’d like to know how I manage to turn this on in the first place. Any clues?
It sounds like you might be using Windows, is that correct? Under Windows (XP?), CTRL+SHIFT can be set to switch keyboard layouts, so it it is possible you have an alternate keyboard layout where SHIFT+/ is mapped to É. Instructions for disabling this keyboard switching shortcut can be found here.
Sorry for the lack of info… I’m using Windows 7. Ctrl+Shift was the solution. See: É? I can do it at will now. 
Thanks so much!