It could be as simple as SDI, but I suspect it has to be something else -- 2010 on the same computer never did this, and I doubt that SDI has changed much. This looks a lot more like a memory corruption issue or a memory leak.
I don't have to run SDI, but I've found it a lot better for the way I work. I'm a PE and I get lots of calls on jobs other than what I'm currently working on. After checking drawings for those calls I tend to hit the wrong "close" button in the upper right. After losing work several times I decided SDI was a better approach for me. I could always write wrappers for open, close, etc., to emulate SDI, but I'd rather avoid that if I can.
Today, no problems. Could be that I didn't stay in one drawing long enough for the problem to appear. I'll post whatever details I can gather the next time it happens.