The DOCX importer read w:tblBorders off the table but never off its table
style, so a table whose style declares none (Word's Normal Table, and the
thesis' Formel-tab around every formula) fell back to the editor's 0.5pt
black default. Resolved per side along the w:basedOn chain, and an
undeclared side is not drawn — LibreOffice writes fo:border="none" for
exactly those tables when it re-saves the file. The ODF importer already
treated an undeclared side that way.
Steffen Becker