When in the Document view, with the Inspector pane showing, and the Synopsis tool running in upper part of the Inspector pane (the default), I enter a line of text and press Enter to get a line feed, and there is no line feed. If I type to the end of the line, the text breaks at the end of word and wraps as expected. When I switch from there to Corkboard mode, the same issue continues (can’t get a LF).
You can change the Return key behavior under Tools>Options… in the Navigation tab. I know it only mentions the corkboard and outliner there, but it applies to the inspector as well.