Guys, there is no “right” answer on this one. However it is abundantly clear that original intent of Markdown was to wrap lines ala HTML, e.g.
this text
is written on two lines
(renders as)
this text is written on two lines
and CommonMark is designed to be as true as possible to the original philosophy of Markdown, only making necessary decisions in the many, many places where the spec was ambiguous.
As noted by @riking earlier:
It is an explicit goal to support a common “switch” that allows linebreaks to be treated as <br> since that is what users tend to expect.
That’s how it works
here too. 
The compromise we have in is that you can indicate linebreak with a backslash character now too e.g.
this text\
is written on two lines
(renders as)
this text
is written on two lines
and at least you can now see why, rather than having to somehow magically infer that there are two invisible spaces at the end of the line…