Just found the original AK thread on AR15.COM. There's a bit more information there. They discuss lots of different parts breakage. It's really not that different than the AR's except for the receiver failures. Bolts, pistons carriers and even barrels have cracked or broken.
http://www.ar15.com/forums/t_4_64/159106_AK_abuse__home_built_version_update_on_Page_6_.html&page=1
http://www.ar15.com/forums/t_4_64/159106_AK_abuse__home_built_version_update_on_Page_6_.html&page=1