The slide is back. You drop a round in the barrel. Then you release the slide, letting it bang home. It is very bad for the extractor. It can also cause the hammer to literally bounce off the sear and drop. The 1/2 cock should catch it, if made properly, should that is.Just for clarification, what does 'dropping the slide on a chambered round' mean? How do you do it? (learning what not to do here).
The hammer should not follow on a 1911 when releasing the slide on an empty chamber. If it does, there is something wrong. Even if it does not follow, it is hard on the sear/hammer. It can damage the sear and the hammer hooks, eventually making it dangerous. Even with parts in good shape, if someone has tinkered with the sear spring etc, the hammer can follow when a slide is released on an empty chamber, even if it does not when dropped on an empty round. The chambering of a round from the mag slows the slide down. When it is released on an empty chamber, the slide hits a lot harder.