According to OASIS OpenDocument standard manifext.xml file should include a version attribute:

http://docs.oasis-open.org/office/v1.2/csprd03/OpenDocument-v1.2-csprd03-part3.html#__RefHeading__752869_826425813

One line in qtextodfwriter.cpp (line 127) is needed to do this:

manifestWriter.writeAttribute(manifestNS, QString::fromLatin1("version"), QString::fromLatin1("1.2"));