Inkscape currently does the right thing sometimes (by pure luck, more or less) -- that particular example does not illustrate a flaw in Inkscape, but in the SVG spec.
In that case Inkscape must stay compliant to the spec. Sorry I didn't notice at first that your previous message was directed to w3c-svg list. It's good that you make our concerns heard there. However, until the spec changes, we must only provide our extensions in a way that does not break our files in other renderers.
On the top path, it looks like the marker's direction is controlled by the wrong control point of the bezier.
The bottom two paths demonstrate that Inkscape computes angles incorrectly -- it averages the tangent vectors of the incoming and outgoing segments, rather than averaging their angles.
Yes, these are real problems that need to be fixed. Please submit a bug report (unless you plan to fix them yourself soon :)