Changing Multiple paths of variable width by % gives wrong result (scaled improperly)

Split out from inbox#355 (moved) (info removed from description)

Steps to reproduce:

1. Select multiple objects of varying stroke width.
   Stroke width measurement automatically goes to %
2. Change the percentage (10000%, 1%)
   Stroke widths are scaled proportionately but are shrunk by a much larger percentage.
   E.g. 1000% shrinks the strokes

This scaling factor should not be present. Its clearly related to the document units

Inkscape Version and Operating System:

1.1-dev (63d65a22, 2020-01-14) and 0.92.3, Linux Mint 19.1

Replicated by @jhofinger (hence me opening it here directly). Workarounds don't work at scale, so marking as high priority