Actually, I've had that happen to me twice. The time with my carry-on was my fault (duh, forgot that I couldn't stick my full-sized bottle of hair mousse in my carry-on!) and it wasn't too horrible because it wasn't packed that carefully to begin with. But the other time was with my checked bag, and at Reagan National in DC, the place where I checked it didn't have a handy table on which to reassemble things--it's a stand-alone machine with a low feed. They ran it through, then pulled it out and had me unlock it, etc. They never did tell me why or what they were searching for. It was totally annoying.