Comment 16 for bug 366744

EDIT to my last comment:

You can work the text properly and it looks fine in Inkscape, but when you save it, either in plain or in Inkscape format, Inkscape doesn't reposition the tspans. By this I mean that whenever you added newlines you have overlapping tspans when you view it in firefox or edit it again in Inkscape.

Example code:
<tspan
         sodipodi:role="line"
         id="tspan13033"
         y="1212.197"
         x="945.15912">✗ J'entre les données et les catégories dans le tableau de bord sur </tspan>
<tspan
         sodipodi:role="line"
         y="1212.197"
         x="945.15912"
         id="tspan3412">monsite.org</tspan></tspan>

So now the only solution as far as I know is to edit all code manually, calculating myself the tspans y values.

My advice would be never to use another format than Inkscape's and not to use scour plugin either. The best option would be to have a custom scouring script that doesn't remove the ability to edit texts afterwards, if this is possible.