Ofnuts, you should consider submitting a bug report upon the fact that the "open-ness" of the curve components of some fonts is not honored when converted to path strokes. I was unable to find an existing bug report on the subject and it is something that GIMP should ideally do correctly in the first place.
I believe the associated code is found in the "gimp_text_vectors_new()" function (defined in
app/text/gimptext-vectors.c). I am not that familiar with Pango rendering and I do not know how GIMP can determine whether the 'RenderContext' should be left open (it may require a change to Pango to expose that information).
If Inkscape handles such text properly (when converted to paths, not merely when displaying it), perhaps it would be worth looking into how they handle it.