I don’t usually post if there’s an update available.
But I think this is a critical hotfix. I’ve seen several posts in CAD forums mentioning that people lost their entire drawings when they work in block editor.
The issue is AutoCAD will replace your drawing with the geometry inside your block. As long as I know, it happens when you work inside block editor and make a save (I guess it includes automatic save).
So if you’re using AutoCAD 2012, I strongly recommend you to download this hotfix immediately.
Download the hotfix here: http://usa.autodesk.com/getdoc/id=DL17244799