On December 2015, one of the APC machines in Texas was selling the "Charlie Brown" holiday stamp labels with an "inverted" ERROR ! The machine uses labels with a pre-printed Charlie Brown design and then adds the barcode, a serial number and the word FOREVER at the time of sale. So while it appears that the printing is upside down, it is only the label that has been inserted upside down, as the machine in the orientation regardless of the orientation of the label. Show above is a scan of the ERROR label and a regular printed one from another date (please note that the scan above show 2 separate strips of stamps). This error was available at this one particular machine from December 1 to 8, 2015 before the problem was resolved (most likely because the machine ran out of labels and the USPS personnel had to insert a new stack of labels, correctly this time!).
1x Upside Down Charlie Brown ERROR strip + 1x regular Charlie Brown strip as shown above.