The behavior you're describing sounds like a bug. The schedule should always resize to fit the objects included. If you're able to reproduce this, I would recommend logging a bug report with all of the appropriate information so we can investigate it.
If you run into this preview issue again, ensure that the "Use Plan View Scale" setting is turned on in the schedule specifications. This setting scales the previews to the size they appear at in plan view, and limits the row height to the tallest preview. Based on the images provided, it looks like that setting was turned off somehow.