I also think this is a Contribute > Bug, and the bad part is that it’s ongoing! no matter I have deleted previous duplicates, I get new ones again. if it helps I can remove the non-official plugins and check the birth of new duplicates.
if it was due to Farsi language, I’d suggest it may be because of some of apparently similar but basically different alphabets that different keyboards are using. for example some devices use Arabic alphabet and some use Persian. and in these keyboards we have ي and ی, which when used in a word one can’t distinguish among them (but they are different in encoding).
but @Pfaffman 's case was for English indexes, bot Persian!