Comment 2 for bug 1129866

The only possible edit you can do to a document in evince is adding/editing annotations, so there are no other cases where this can happen. If you try to close a document with unsaved annotations, a dialog asking you to save first pops up.

In any case, this can certainly lead to unintentional loss of data (edits) by just one mis-click, so in my opinion, it is certainly a bug.