Comment by timonoko

As I recall Koreader did not recognize that there are basically two versions of TXT-files.

In the first one paragraph is marked with single Carriage Return.

In the second one the paragraph has two CRs and all single CRs can be replaced with space.

Annoying but bagatel:

    sed ':a;N;$!ba;s/\n\n/XYZ/g'|sed ':a;N;$!ba;s/\n/ /g'|sed 's/XYZ/\n/g'