I hope this was just a glitch, but I did a bunch of renders last night, and in the morning, when I looked over the screenshots all captured with "P" in Keyshot 2, they all included the Options panel that was in the foreground, often obscuring parts of my subject....
grr.
I have not seen / heard of this issue before.
It hasn't happened again, but just to be safe, I'm more conscious of moving the palettes off the scene.