In the screenshot, you can see some places where the subsurf will have some edges, but it won’t finish the whole loop-cut.
Why does this happen, and how can it be fixed?
I am using the latest CVS version, so is it possible that there are some buggy stuff in there?
I think they’re there, they’re just not drawn in your the 3d view. If you apply your modifier you’ll see them.
You’re in wireframe view, normally the view won’t show every edge there is but switch to solid mode and you’ll see them.
There’s a button in the object panels for wireframe labled slower draw or something similar, clicking that will eventually force all edges to be drawn