Plain rendering glues message-box titles and adjacent text together

rendered=true (plain/1.0) output concatenates the generated title of info/warning macros onto the previous paragraph without a separator, and drops images to blank lines.

Expected: A line break before a message box's title (and ideally a marker such as [Information]), so quoted text does not contain glued words.

Actual: Glued words. An agent quoting the plain render will reproduce them.