I note the perforations along BOTH the right side and the bottom seem to jump slightly. Clearly the perforation "bridge" at the right side shift is longer than normal.
I don't buy into the perf wheel jump theory (or a paper shift theory). What are the odds that it also happened along the bottom edge on the same stamps?
Occam's razor. While not having the stamp in-hand, I would suggest a simpler theory. The stamp was printed normally, then somehow a very small diagonal crease occurred in the sheet during drying/stacking process. The creased sheet was perforated, sold and used. It has since been fully soaked and carefully pressed-out to be unnoticeable today. It would be interesting to see if a crease is visible in fluid.
Consider the following picture with the two diagonal lines representing the double fold of a paper crease. When unfolded, the perf rows jump, but are the same gauge for each half, and depending on the hit/miss pattern, the bridge between holes can be longer or shorter by chance.
That's my take without in-hand study. Thoughts?