I have found out a problem with the answer fraction value generated by
the Moodle xml converter :
the code generated for a third of point was <answer fraction="33.33">
whereas it should have been <answer fraction="33.333">
(note the third decimal)
Reference :
http://docs.moodle.org/en/Import_questions#Match_grades
BTW, many thanks to Olga, Yulia and Alexandr... Your xml converter is
wonderful, I just wanted to save other users some time by sharing this
info.