I recently deleted a note that was part of a shared notebook created by a colleague. I just figured that if something goes wrong, I can always fish it out of the trash. It turns out that it never makes it to the trash. It just disappears! Now whenever I Sync, it tells me 'sync failed due to unexpected behavior at client side". All my notes do sync though, it's just that that particular note from the shared notebook doesn't ever come back, and I think that's why the error appears. Hopefully Evernote addresses this soon.