Comment 5 for bug 811862

It appears that the value 'central' is miscalculated for dominant-baseline. You specify the baseline offset as '0.5 - _descent', however the spec specifies "a computed baseline that is at the center of the EM box" (i.e. just 0.5).

Refs:
https://gitlab.com/inkscape/inkscape/blob/master/src/libnrtype/FontInstance.cpp#L808
https://www.w3.org/TR/SVG11/text.html#BaselineAlignmentProperties