The default setting on an account is to save new content to the Knowledge Base. New content means you didn't use the search engine to copy responses out of the Knowledge Base. This could be content you authored or copied from an external source.
Note: Administrators can read about editing the settings here.
When you use content out of the Knowledge Base, the Save to knowledge base button turns itself off...so we don't put duplicates in the Knowledge Base.
If you modify a response you used from the Knowledge Base, you will have to turn the button on to save the new variation. The system doesn't make a decision based off of an edit, as this could be one word, a sentence, or something very material.
If the response is approved, you can go back and click the Save to knowledge base button. That will push the question/response pair into the Knowledge Base.