RMB and 'Esc' keep starting a render!

I am quite an advanced Blender user, and this has suddenly popped up out of nowhere!

You know when hit ‘alt-D’ to instance/duplicate objects then you drag the objects away from site of duplication to see that the duplicates are there, then you press ‘esc’ or Right Mouse Button to let them go back to their original location ?

Well, when I press the RMB or ‘Esc’ it triggers a render AND doesn’t snap the objects back to original location! It is very annoying. It has only just started doing it and has never done it before. Have my key commands somehow become remapped?

Iopen a new default scene and try to do the same thing to the default cube, and it doesn’t trigger a render. SO it must be something different about the file in question.

Aha! I was because ‘Auto Render’ was ticked in the Compositor window.