The command <TT>regsub $markdown {\n}</tt> in proc [convert] replaces
the first CR/CR+LF in the Markdown text with the literal string {\n}.
This cannot be the intended behavior.  It would make sense for it
instead to replace every occurrence of CR/CR+LF with \n.

Here is how this bug was fixed in Tclssg, which also includes a fork
of the Caius Markdown package: