Comment 2 for bug 680347

Once the values for the four margins have been written to the SVG document for later reuse, 'Fit page to…' only takes one changed margin value into account when clicked:

  <sodipodi:namedview
     (…)
     fit-margin-top="40"
     fit-margin-left="15"
     fit-margin-right="15"
     fit-margin-bottom="50">

If those four 'fit-margin' attributes are deleted from the SVG file (using e.g. the XML Editor), the next 'Fit page to contents…' command again sets all four margins with one click.