I had noticed this several times:

Nothing in trash.
Clone a drive.
Boot to the cloned drive.
Re-start, and boot back to the Macintosh HD
Notice "Recovered Files" in trash.
Emptying trash seems to have no ill effect.
No, I don't remember exactly what they are, but I seem to remember there being a whole hierarchy of folder structures, perhaps the root of which is something like ETNW, or something like that.
I notice that it either doesn't happen or it's less frequent if I use Disk Utilty to make the cloned drive. If I use CCC or SuperDuper!, it seems more likely to happen. Again, there seems to be no harm in emptying the trash.
Any idea what's being recovered and why?