Duplication/replication of keywords in term list

I am using Endnote X3 on a PC. I have encountered a problem where some keywords appear multiple times in my keyword term list. I checked to be sure all cases of the keyword were spelled and formatted the same (e.g. no hidden spaces). In an attempt to get rid of a duplicate, I went to the 5 citations where the keyword was used, and retyped the offending keyword, allowing the program to autofill the final keyword (assuming it would autofill the same way in all cases). Now I have not two, but 5 replicates of this keyword in my term list. Any advice or suggestions on how to get it back down to one, and how to avoid the occasional appearance of duplicates?