Problems with "format bibliography" in EndNote Online

EndNote X7, Word 2011 Mac

If I choose to work from EndNote online, the Format Bibliography and Insert References is not working properly. I see duplicate references when they aren’t duplicated, and when I choose multiple references to insert, it often inserts the correct references but after I do a format bibliography and unformat the references again, it changes one of the references to another reference. 

I changed to working with EndNote directly instead on on the Web, and things are working normally again.

I don’t undertand what is going on. My enl file on the Mac is synced with the file on the Web, and neither one shows any duplicate references.

Should I not work with the Web file at all, just sync the references so that my co-author can get to them when he logs on to his EndNote Web and revises the article we’re working on? Or should I send hi my updated enlx file each time I send a revision to him, and vice versa?

Hope I’ve been clear–no doubt there will be questions.