If it has been properly tested or not is of no real relevance anymore, because as we have it right now, it's on live. If it's a bug or not is questionable, we don't know for sure if it's intended for the crafting window to totally reset after each skillpoint up (or now for every 0.1), it really makes no sense for anything else than new recipes learned. Because of this I'd say it's "not working as expected" and as such a very possible bug.
A software bug is the common term used to describe an error, flaw, mistake, failure, or fault in a computer program or system that produces an incorrect or unexpected result, or causes it to behave in unintended ways.
It's definitely unexpected and I'd say that it causes behavior in unintended ways as we have it right now in my opinion thats a flaw. That would make it a bug, by definition. Bug and feature are just two sides of the same path, as we cannot know for sure how it was intended to work, that justifies this here.