I have a view with a Mapper that indexes on a text field within the document. I changed the logic slightly (sometimes I was transforming the field I used as the key before emitting it), and incremented the version. I noticed that when I ran the View the next time, one document (at least, I suspect more) appeared in the results twice. For fun, I incremented the version number twice more without making any changes to the Mapper, and each time, one more copy of the document appeared in the result. The only interesting thing about the key was that it contained only CJK characters, as it’s a Chinese name.
I called View.deleteIndex() and that removed the duplicates upon regeneration of the index.
Oops, it turned someone had accidentally reverted us to use 1.2.1. When I fixed that and started using 1.3.1 again, the problem went away. Sorry about that!