A later printing of this issue. Scott indicates that "most examples" of this sheet are bent at the upper right corner. The UPSS similarly states that "Many if not all sheetlets have the top right corner slightly wrinkled due to transit." Over the past 34 years I've sold a few hundred of these, and they all had the crease. They were also all non-fluorescent.
I recently found a small group of these, and checked them for FLUORESCENCE, as I do with most modern cards. It was only then, after I noticed the first Fluorescent cards I had seen in 34 years, that I saw they were also crease-free. I've also handled some First Day Covers, and from this I believe that the First Printing was Inert & Creased and that the Fluorescent/Straight cards were from a later printing.