will return two results in my case. A series and the one episode it belongs to.
will return nothing. Obviously, it should return the episode.
The firs one should really return the episode, but to get only the episode it doesn't make sense to use the series.xml endpoint, using the episode.xml endpoint makes much more sense and I'm pretty sure that no one is using it like this.
I agree with you about the first issue. I guess the idea of making it possible to disable series (the series=false option) is an old API remainder and is not used anymore. To get rid of this bug, we could also decide to not fix it, mark the series option as deprecated and to be removed in one of the next major releases and then, at some point in the future, remove it. Any thoughts about that?