Here is the official word from BD'd QA Manager:
Axles of different Length
the short version of the explanation is that we increased the length of the
axles on the #4 to allow for a bit more clearance. This was an in-line
change. Both iterations were tested extensively and performed safely and
well in all situations, however we decided that a little more room for
clearance between the cam lobes, the side plates and the center cross bar
allowed for the cam to function a little smoother especially when gunked up
with dirt after sitting at the base of routes, like at Indian Creek, etc.
so yes, there are cams in existence that have different length axles (of
course one cam wouldn't have two different axles, rather some cams on your
store shelf have axles that are longer than other cams on your store shelf).
All units are safe, correct, and good to go.
Clearance between cam lobes, side plates and cross-bar
What you're also seeing, and as I said earlier, is related to the axle
length - is the amount of play, or the amount of side-to-side movement of
the lobes on the axles
again this is intentional and designed to allow the cams to function
properly in all conditions.