Thanks for the tip. It is not a big deal but a little clarification because I am happily using Discourse other than this one.
What I learned from this topic is that the Discourse’s new rendering engine changed the default behavior of the width/height settings. In fact I am glad you confirmed that it is the new default. I can manage my issue via CSS, although I need to learn it.
But as an end user, I want to provide it as a feedback that the current version’s width setting will trim the images if it’s wider than topic body. I may not be able to say it is major use case; but it is better be explicitly explained for other users.