Comment 4 for bug 1671691

UPDATE:
tl;dr - If you select the 'viewBox' option when opening a pre-0.92 drawing then the issue of inability to adjust display units does not present itself.

After implementing the solution I mentioned above on several drawings, I realized it has the side effect of enlarging your drawing A LOT! It turns out the issue of display units is caused when choosing the "Scale Elements" option of converting old <0.92 drawings to new 0.92 format. If you instead select the 'viewBox' option then the issue of inability to adjust display units does not present itself.