Posted by Bruce Kahl on March 15, 2000
In Reply to: A guess... posted by ESC on March 15, 2000
"Bones" in this case is short for boners. Although boner has other meanings, a boner is defined as a mistake. This meaning has fallen out of common usage but was once widely used.
So if there is a "bone of contention" between 2 people then maybe it is a past mistkake that is being contended!