Well, here's something I've never seen before...
This is the cover to my old copy of Federal Comics' Tales of the Legion of Super-Heroes #14:
It's a nice copy in decent condition. The price sticker on the cover is a bit unfortunate as it has left a discoloured imprint on the inside of the cover, and it has prominent age spotting spreading into the book, on the covers, but it's fine for my purposes, which is as a placeholder in my collection, not being a series I'm particularly interested in. I read the first 12 volumes of the Legion of Super-Heroes Archives, which I thoroughly enjoyed, but the Federal series has accumulated over the years in the Junkyard more by accident than conscious collecting.
The other day this copy fell into my hands:
It's in a similar grade to my existing copy, trading a crudely scrawled pen mark for a sticker, and with little signs of spotting, but is otherwise identical in grade to it's predecessor. I could tell this much by the cover scan in my database, but as is my habit, I pulled out my old copy for a side-by-side comparison to see which copy would make the cut as the representative in my collection, and which would be traded or sold.
And I'm glad I did, because what I found was that the cover of the new copy was actually incorrectly attached to the wrong comic - rather than opening to the splash page for a chapter of Shadows of Future Past, I was met by the pencils and inks of George Perez on the splash page of The New Teen Titans'' The Judas Contract Book 2: Betrayal! Yes, the cover to Tales of the Legion of Super-Heroes #14 is wrapped around the pages of Federal Comics' Tales of the Teen Titans #13!
Obviously this is an unintended error at a particular stage of the printing and binding process. It's understandable in one respect - the rear covers and inner cover advertisements and letter columns to both Tales of the Legion of Super-Heroes #14 and Tales of the Teen Titans #13 are identical, and both were published in February 1986. It's also probably no coincidence that this period marks the tail end of Federal Comics as a publishing entity, so this error may be symptomatic of a general waning of quality control.
So inspect your copies carefully - you may have a variant lurking in your collection. And if you only have the legitimate version, hunt down the variant quickly, before someone alerts the blogosphere to its existence and prices skyrocket on the variant market!
PS Photos would help illustrate this anomaly, but the only way to demonstrate this visually is to fold the covers to reveal the adjacent splash page of each issue, and I'm not about to damage my books to do so. If and when I get ratty copies of each I'll do so and update this post - in the meantime, ya just have to trust me.