I successfully tested libreoffice in xenial-proposed (libreoffice/1:5.1.6~rc2-0ubuntu1~xenial4) with the instructions in comment #51 (xenial ➞ xenial-proposed ➞ upgrade to bionic without disabling -proposed).
I successfully tested libreoffice in xenial-proposed (libreoffice/ 1:5.1.6~ rc2-0ubuntu1~ xenial4) with the instructions in comment #51 (xenial ➞ xenial-proposed ➞ upgrade to bionic without disabling -proposed).