2006 Disney #4025-8 Sheet With Rounded Right Corners

I am not sure what I have. All but one of these sheets in my stock have normal square corners. However, one sheet has rounded upper and lower corners on ONLY the RIGHT side.

There is no doubt that the rounding was done with a corner-rounding device, but of course I don't know WHO did it. It came out of a sheet accumulation/collection; no others had anything like it.

I asked the Scott editors if they were aware of any special version of this and they said that they were not.

Do I just have a damaged/altered item or was this from some special folder, book, promotion?

Thanks.

A scan of the stamp(s) in question would be helpful.