Quentin,
If you have a blade that actually "hops" over another one I believe the lens may have been serviced by a camera barbarian. The orientatiion of the top blade is correct, but unless the other blade is the bottom blade I believe it has either been incorrectly assembled, or when a lens group has been removed something got in there & bent it.
Does it look like the bottom blade is actually causing a wear pattern on the blade beneath it? That would be a good indicator of something being wrong.