Run and Preview modes use the Lectora rendering engine. They do NOT use a browser which renders pages differently. To work on this problem, view them using the Preview in Browser button OR publish to HTML on you PC.
I have seen that problem before but do not remember the solution. Here are several things to try.
1. Cut all the text from the text box and paste it back UNFORMATTED. Then try viewing in a browser.
2. Simply add a blank line after the last paragraph.
3. Click in the paragraph, right click and select >Paragraph > Paragraph spacing and add some space after the last paragraph.
