I explain the things badly, in English
The XHTML produced by format ODT, in OpenOffice, is valid. But, when one uses the XHTML produced by a file ODT in OpenOffice (Export) with Calibre, the result is not the same one as when one uses directly format ODT for th same file, with Calibre.
To understand, here 2 pictures, the same text, with ODT, and with XHTML produced with OpenOffice:
Epub Calibre with ODT:
https://www.mobileread.com/forums/att...1&d=1233436953
Epub Calibre with xhtml:
https://www.mobileread.com/forums/att...1&d=1233436953
Appearance is not the same one, the margins in particular (not to take account of space between paragraphs, it is an error which I did)