As you know, when you edit a post in SE communities (like SO), sometimes your edition will be a new version, and sometimes else the current post will be just updated.
According to some tests, I figured it out:
when there is a comment under the post after the last version, it will create a new version if you edit the post.
When 10 minutes passed since the last edition, then it will create a new version if you edit the post.
Anything else?