Setting cluster=true is still rendering nodes without a cluster box

[abhijithda]

Setting cluster=true is still rendering nodes without a cluster box via this package. Whereas in the playground, it working fine...
Similar issue with other attributes like bgcolor...

Sample

digraph "" {
	subgraph test {
		graph [bgcolor=red,
			cluster=true,
			label=test,
			style="filled,rounded"
		];
               a -> b
               c -> b
       }
}

Getting:

Expected:

[abhijithda]

Looks like if the subgraph name contains cluster prefix, then the cluster box is appearing. Otherwise, the cluster box isn't appearing.