The attributes table:first-row-end-column, table:first-row-start-column, table:last-row-end-column, and table:last-row-start-column are deprecated in ODF1.2. The new feature table template in Writer should not write deprecated attributes. The corner cells are already treated in the loext extensions.
These attributes are not written for the table templates of Draw/Impress.
Setting to NEW.
Unfortunately these attributes are not optional. So they indeed needs to be written. LibreOffice needs to wait till ODF 1.3 before they can be removed.