From #40 of issue 76113 <crbug.com/76113#c40>

You only need to do some minor change to a text to trigger this. For example, you could write that "these cookies are sugar-free" and then later change that to "sugar- and lactose-free", and if the text was wrapped at the hyphen, you now have an extra line break:

these cookies are sugar-
 and lactose-free

Or, you could first write "these cookies are lactose-free" and then add the "sugar- and ". If the temporary state "sugar-lactose-free" is wrapped after "sugar-", you end up typing the next space at the beginning of the next line, again producing the same result as above.

This problem is often seen in Finnish forum posts, where hyphenated words are quite common.