What would cause my barely used green bearing to do this?

I installed these dutchman axles a few years ago, and they have very few miles on them. I pulled them out today to replace the pumpkin, and this is what I find. What in the world would cause this? This is just the one axle.



Full size pictures
http://www.semisynthetic.net/kill-9/gallery/albums/userpics/10001/20210502_155032.jpg
http://www.semisynthetic.net/kill-9/gallery/albums/userpics/10001/20210502_155059.jpg