### graph vertex ~~labeling~~labelling

I have a graph (poset actually) that has a rational function labelling each vertex. I would like to show just the edges and the vertex labels. If I try to set `vertex_shape='None'`

I get a crash deep in matplotlib. If I try anything else I get the marker symbol printed over the label. For example

```
P = RootSystem(['A',3]).root_poset()
P.show(vertex_color='white')
```

Will show the graph with circles over the labels. If I shrink the labels, then the edges cover the ~~labels.~~labels.
If I do

```
P = RootSystem(['A',3]).root_poset()
P.show(vertex_color='white', vertex_shape='None')
```

there is a strange crash.