Connectors with startdir between 13-15 get the wrong dockend

[rockersuke]

For some reason connectors whose startdir position is in the range 13-15 will have their dockend point to an innexistent location 0.
They'll display correctly on screen, so most of the times you'll only notice something is going wrong when trying to export to some adventure system source code. I tried Inform 7 and the rogue connectors would simply be ignored.