I'm having the same problem in the Mac version of Evernote. It only seems to happen for old notes (those created on Nov 10th or before), not new ones, and only when I use Evernote 5 for Mac. Did something happen on Nov 10th that changed the way notes are stored in Evernote? Maybe a change to the ENML? I worry that it's actually making modifications and potentially losing data, so I don't want to sync until I know for sure what's happening.