Graphviz edge label position - graphviz ignoring label positions when control points not defined for edges

Question

Graphviz (using neato) ignores label positions when control points are not defined for edges.

I can brute force my way to positioning the labels, but I'm doing this in ignorance of the real problem.

Is there a way to stop graphviz overwriting lp, xlp in edges that do not have the curve control points pre-defined?

Why isn't lp working on nodes?

I can position edge labels only if I position nodes and edges, and define edge curves

# manual_edge.dot
digraph G {

  A [label = "A"  xlabel="a" pos="0,100" lp="200,100!" xlp="300,100!" ]
  B [label = "B"  xlabel="b" pos="100,0" lp="200,0!" xlp="300,0!" ]

  A -> B  
    [pos="0,100 0,0 0,0 100,0" ] 
    [label = "A->B"  xlabel="a->b" lp="200,50!" xlp="300,50!" ]   
}

Defining positions is easy enough, defining curves is a bit painful. If I don't do it - the edge label positions don't work:

# edge.dot
digraph G {

  A [label = "A"  xlabel="a" pos="0,100" lp="200,100!" xlp="300,100!" ]
  B [label = "B"  xlabel="b" pos="100,0" lp="200,0!" xlp="300,0!" ]

  A -> B  
    [label = "A->B"  xlabel="a->b" lp="200,50!" xlp="300,50!" ]   
}

When I export the dot output I can see that when I don't define the edge curves, my label positions are being overwritten

$ dot -Tdot -Kneato -n2 -o ./output.dot ./edge.dot

    A -> B   [label="A->B",
        lp="30.532,60.968",
        pos="e,84.997,15.003 15.188,84.812 31.877,68.123 58.839,41.161 77.877,22.123",
        xlabel="a->b",
        xlp="33.032,45.968"];

to work around this behaviour, I'm putting my values in nonsense attributes that survive processing and using regex to clean up the file before passing it back to neato:

...
[label = "A->B"  xlabel="a->b" zzzzl="200,50!" zzzzxl="300,50!" ]   
...

...
    A -> B   [label="A->B",
        lp="30.532,60.968",
        pos="e,84.997,15.003 15.188,84.812 31.877,68.123 58.839,41.161 77.877,22.123",
        xlabel="a->b",
        xlp="33.032,45.968",
        zzzzl="200,50!",
        zzzzxl="300,50!"];
...

After converting zzzzl to lp, and zzzzzxl to xlp diagram works. This is because when attributes are set multiple time the last value is used

dot -Tpng -Kneato -n2 -O ./output.dot

This gets me what I want, but it's a bit longwinded. Is there a way to stop graphviz overwriting lp, xlp in edges? Why isn't lp working on nodes?