When the delete button DOESN'T delete

I recently hit the *delete* button instead of the playback button and expected the confirmation dialogue to appear. (I wanted to blank the screen and return to *capture* mode).
I had also forgotten that I had zoomed the image and not restored it to normal size. I was very surprised when the image resumed its normal size instantly.
Hitting *delete* when viewing a zoomed playback image restores the image to normal size on both *ist DS and the K5. There doesn't appear to be anything about this in the manuals of either. ........ it's very convenient!

David