what exactly do you mean by "duplicated bibliography"?

For some reasons, there are two different versions of that article inserted in the paper. I can't tell you how exactly that happened--could be one from a group one from a personal library, could be that one is embedded in the document from an entirely different library, there are probably a couple of other ways. Also, if you or your co-author worked with an exported version of a library that'd have happened.

I don't think there's an alternative to going through the text and replace the duplicates: Insert that citation from your library and see if it turns into 2007a or 2007b.
Let's say it's 2007a. Then replace all instances of the 2007b version of that paper.

it's not an existing problem with Zotero -- it's the result of user error.
In the thread you link to, e.g., it was using export/import to move libraries between computers.

we can't fix something that we're not aware of as a bug. You're the only person reporting this among hundreds of thousands of Zotero users, so it's almost certainly something about your workflow.

If you're using Word, you can press alt+F9, pick one of those citations that are duplicate (in the text) and copy the whole field code for both of them here and we'll likely have a better guess of what happened.

That's odd (on Mac this would be Opt+F9), but you should be able to use

Go to Word Options. Click the "Advanced" tab and scroll down to the "Show document content" section. Right above the "Field shading" box, there is an option "Show field codes instead of their values." Check that.

via http://www.justanswer.com/mac-computers/7hl56-reason-word-mac-started-show-hyperlinks.html#ixzz3USsBQ6t6

And by "both" I mean the field code for a citation that comes out as Hickok(2007a) and for one that comes out as Hickok (2007b).

Just wanted to echo Adam's issues. I had many many many of these problems with a proposal I just finished. Did not have time to debug the issue or check codes. just hand edited the bib and the references. (much easier than deleting them.. search and selective replace for a) b) c) and a; b; and c; was bearable.

My issue also occured with many authors editing things, and a few MS word merges (some Mac some Windows) merges so maybe something there broke the codes, so the next addition of a reference though it needed a new one.

Anyhow just letting you know its not just Life'1944s problem.

A very useful feature would something that lets a user select 2 bib entries and say merge them .. (like you can in the main tool) and have it find and replace the 2 different labels with one consistent one. Then, no matter why it happened, it would be easy to fix.

I am not sure if this discussion is still relevant, but in the current version (2021) duplicated bibliography entries in collaborative documents in Word are most commonly caused by adding citations from different sources. For example, some might come from a users "My library" and some might come from one or more groups that a user is a member of. Even though these entries may have identical data, Zotero will treat them as different. Additionally, if you are working with a collaborator and the collaborator has added an entry that you do not have in "My Library" or in a group that you are a member of, that entry will persist in the word document in the zotero-inserted field codes for that reference. If you then later create a shared group for the project and add the same reference from the shared group, you need to delete and re-add the earlier reference. Otherwise, the bibliography will have separate entries for the same, identical reference. There are two ways to identify references that are persisting in the document without pointing to a shared group. One is to attempt to edit the citation; at the bottom of the edit window a button should appear that says "Open in ". Alternatively, if you set field codes to visible in Word, the field codes will have the word "user" (plus a numerical ID) as opposed to "group" (again with a numerical ID) as the source of the reference.