Problem with `graphviz_chart` when using subgraphs

Using Streamlit
1

Hi all. I am using st.graphviz_chart to display a DOT string which uses Clusters | Graphviz (subgraph) to draw boxes around certain nodes. When using the following DOT string in, for example, the Graphviz online editor at Graphviz Visual Editor (magjac.com), there are 2 subgraphs drawn. However, when running as a local streamlit app, the subgraphs are not drawn. Can someone help figure out the reason for the discrepancy?

st.graphviz_chart('''
    digraph {
        run -> intr
        intr -> runbl
        runbl -> run
        run -> kernel
        kernel -> zombie
        kernel -> sleep
        kernel -> runmem
        sleep -> swap
        swap -> runswap
        runswap -> new
        runswap -> runmem
        new -> runmem
        sleep -> runmem
        subgraph sub_1 {
            cluster=true
            run;
            intr;
            zombie;
        }
        subgraph sub_2 {
            cluster=true
            swap;
            runswap;
        }
    }
''')