@Chris: the output of the dpkg command you provided in #3 suggests not all the packages were built at the time you tried it (you only installed the architecture-independent packages from the update), can you try again and confirm that libreoffice uses the breeze theme by default, on Lubuntu/LXQt?
@Chris: the output of the dpkg command you provided in #3 suggests not all the packages were built at the time you tried it (you only installed the architecture- independent packages from the update), can you try again and confirm that libreoffice uses the breeze theme by default, on Lubuntu/LXQt?