I've been using SW for about ten years, and I've had this happen maybe a couple of times in those ten years, but ever since we started using 2013, I keep losing my references to models. Faces, edges, cylinders...I will have everything ship shape, then I close the asm, then when I open it again, I'll have a few red marks in my tree, caused by lost references. For instance, I extrude a block up to a face on a part ( so far these have been parts from weldments that I have imported in as step, iges, or parasolid files), and when I open the project back up, it has lost the reference to that face, along with any references that the sketch has to the imported model. . A few other people here at work have had some minor issues with this, but I can pretty much say that about 80% of the time when I open a project back up, it will have broken references. Like I said, I've maybe had this happen once or twice in the last 10 years. Anyone else out there having this issue since upgrading to 2013?