With child's mind I expected two notes, like two colors, to mix as a new one. I tried more. However many notes I played, each note remained itself. Then and now, this has seemed to me a marvel. The Vose taught mechanics too.
Uprights have a joint in each action that comes apart when the glue fails.
It's easy to fix. I learned at age eight, doing it routinely for years. You take the front off the case, undo four thumb nuts, and lift out the works. Two screws release the broken action. The broken joint is two pieces of hardwood machined like metal, fitting snugly.