Incorrect apostrophe character in MS Word 2011 on Mac
After updating OS X to 10.9 and opening Word for the first time since the update I encountered the same problem. I spent half a day testing all the suggestions put forward here and in other forums responding to the same query (including checking autoformat preferences/searching for font duplicates/verifying fonts/testing in new mac user account/repairing permissions etc.) with no luck.

Finally, I deleted the Cambria font from the Font Book and reinstalled again. I reopened Word and tested and the problem seems to have disappeared.

I'm using OS X 10.9 and Word for Mac 2011, v14.3.8.