> The issue is empty lines that serve as paragraph separators and that may 
> appear due to expansion of a macro or due to skipped export snippets. 
> Perhaps transcoders of other elements, e.g. links, may return empty 
> strings as well.

Right. This is a special case in MD where blank lines separate
paragraphs. Just like in ox-latex, where we fixed exactly same thing
reported in https://orgmode.org/list/tufdb6$11h2$1@ciao.gmane.io

It is also a side effect of the fact that newlines are not considered a
part of the Org markup objects.

I do not think that we need to handle this Org mode-wide (it will be
difficult and will likely cause breaking changes). We can only adjust
the export backends sensitive to blank lines.

See the attached tentative fix.