I think it was military. Officers had to provide their own uniforms so regs on a lot of stuff went out the window. I've seen a couple with that back on it.
The quote from the other forum was from Cannonball Guy. You don't find him misquoting very often. His point about the shank is valid. That button was discontinued in 1902 and that method of self shank had not come along then. Military buttons are often copied, especially the navy ones.