Sudden repeat citation

Everything works perfectly normal with EndNote in Word, but with this one particular citation this is what happens: {Ziolkowski, 2012 #646;Ziolkowski, 2012 #646;Ziolkowski, 2012 #646;Ziolkowski, 2012 #646}. I don’t think I’ve done anything differently than usual; it’s the same output style, field, the same file, the same endnote library…Does anyone recognize this problem?

Are you sure “Instant formating is on” and not off?  That option is on the Endnote ribbon.  You can also try “Update citations and bibliography”.  What you are seeing is Endnote’s Temporary citation and not the CWYW version.  

Yes, when I ‘update’ I simply get that reference repeated five times over. So that can’t be it.

Is it grey (like a formated citation)?  Sounds like you may have inserted it into a “field”  and corrupted it.  I would delete it and a word either side and retype those words and try reinserting the citation.  (just noticed it was the same citation, mutiple times).  

Edited: 

If that doesn’t work, and you have the library it was created from, you can make a copy of the document (very important in case it messes up) and try the Unformat, remove field codes, reformat trick described in more detail here – http://endnote.com/kb/81143

That did the trick - I think I inserted the reference in a field code. Thanks!