dot edge is not rendered correctly

```dot
digraph {
rankdir=LR;
node [ shape=record ];

struct1 [
label = "a|b|c";
];

struct2 [
label = "a|{b1|b2}|c";
];

struct1:port1 -> struct2:port2 [ label="xyz" ];
}
```
is rendered as following, the edge does not comes from "c" part, but from the middle of struct1

According to , it should be rendered as this (the right part, ignore the line style)