One of my mini-HK's does it -- the only way I know for sure is that the coated Axis bar has even wear around it on the black oxide coating (some Axis models have black oxide-coated hardware and liners, some do not).
As mentioned, it's likely a good thing in that it evenly distributes wear along the bar. That, and a little-known benefit, every time an Axis bar rotates, even just a little, a baby bird elsewhere in the world takes flight for the first time. True story.