Postcard Setoff , Common?

I just notice that what I had though were setoff cancels is actually the setoff of the back of the postcard. I suppose it happened with postcards as often as it did with stamps, this is the first I have seen.
The postcard front and back and a crop from original scan (at 64%)

When a canceling machine operates properly, it is only triggered to print when there is a mail piece passing through it. Sometimes it is out of adjustment and it prints constantly and makes "blank" imprints which are on the rear roller which then transfer to the back of the next mail piece. It is not transfer from touching the wet ink on the next mail piece.

Rather than the cancel, I believe littleriverphil actually is referring to transfer of the FOR SALE printing in the "This Space for Correspondence" area, which is barely visible (in reverse orientation) in the upper right portion of the lower image he provided. This effect could certainly occur on any postcard where blank picture postcards are prepared first, then printed with commercial information in the same area. The use of large bold type, accumulating a lot of ink, certainly caused setoff of FOR SALE in this instance. It would seem likely to occur for other similar twice-printed cards, and I will be double-checking any that I have.

Chris

The OP would have to clarify for then.

Yes, Chris Is correct, I am referring to the reversed For Sale seen on the upper right of the card and much cleared in the cropped scan ( last pic). Have seen lots of heavily inked cancels set off like of the upper left of the card, but thought the set off of the card back was unusual.