When I create a QTextDocument and insert a table, important information is set through a QTextTableFormat instance. That information gets lost when QTextDocument exports an ODT file, while being preserved in HTML and PDF files.

In particular table borders and cells padding (and maybe other details) are not set in the contents.xml file that constitutes the core of an .odt file. Therefore opening this file with an editor (I used Microsoft Word, Apache OpenOffice and LibreOffice) results in tables rendered with the default settings of that particular editor.

I am attaching some minimal code that produces three files - HTML, ODT and PDF - starting from the same QTextDocument object.