Most times, it's a simple error in the printing process (a sheet or stack of sheets go through upside down) and you get the card in the upper left corner on the front with the card in the lower right corner's back). This accounts for almost all of the wrong backs for standard cards that exist.
Now, in this case, things again, are little different. From what I unerstand, the process for putting together a MEM card involves actually attaching the MEM to the card back and then attaching the front (maybe the process is reversed, but I doubt they attach the MEM to the front).
The next question on these cards are - is the MEM from Loney, or from Zimmerman? But this did look like more than the simple printing error, which is I why I added it to the database.
-- Dan --
Note: Please see my profile for more info regarding trading (section updated 3/4/2024). I have added a large portion of my inventory to the site, and currently have trading turned on (details are in my profile).