Yes, when I say “original” format I mean the initial format which was imported. In fact, I think it makes more sense to call it “initial format” to avoid overlap and confusion with Calibre's idea of what “original” means; thanks for noting the terminology problem.

In my case, I almost always want to convert from the initial format, regardless of what has been done in the meantime, and that's what my patch allows me to do. In fact, I've modified it so that the conversion dialog always chooses the initial format by default, regardless of preferences or saved conversion settings.

So in the above example, MOBI is the “initial format”, tagged as such in the GUI, and used as the source for conversions, all without manual intervention. I don't claim this is useful for the majority, but it is the workflow that I prefer.