Comment 20 for bug 1365451

it depends entirely on how you make the switch from mm to px as document units. In previous versions of Inkscape, in development versions, it was possible to do a live switch from mm to px using the Document Properties dialog. In current trunk, that live switch is no longer possible. So if you open the Document Properties dialog and switch Display Units from mm to px, then the document units will still be mm, despite what the dialog says.
    The simplest way to use px as document units is to load the file share\templates\default_px.svg directly into Inkscape and then continue with your test.