The problem with split rails isn't the interface between the 2 having a bump, but the pieces not being perfectly in-line/in-plane. When that happens you can only make one side of the split rail perpendicular to the mitre slots/blade. And once your fence straddles or crosses the joint connecting the split rail, it will no longer be in perpendicular alignment.
Typically not a problem for most people who don't use the fence to the left of the blade. Can show up when you're doing a close cut to the blade as the split-rail joint is normally right at the blade. If your split rail does this, you have to disconnect and reconnect until you get them perfectly in-line. Then you can worry about the "bump".