Typically when you reflow a document it breaks it out of containers and makes width 100%
Images are placed on their own line following text containers (way at the end often)
Other columns/side containers will then later be displayed after the paragraphs have ended.
Are you sure the images are just omitted? They may be, because there is no way to show them properly when you reflow a document that isn't tagged for reflow, just like there isn't a way to properly show multiple column/table documents.