concentrate attribute does not work between nodes of different clusters

[bugriy]

If I render graph without clusters everything goes fine. 2 way connections turn into 2-way arrows according to concentrate = true attribute.

`
ndf1 <-
data.frame(
id = c('a', 'b', 'c','d','e', 'f'),
label = c('a', 'b', 'c','d','e', 'f')#,
# cluster = c('1', '1', '2', '2', '2' , '3' )
)

edf1 <-
data.frame(
from = c( 'f', 'c', 'f', 'a', 'd' ),
to = c( 'c', 'f','a', 'f','e' ))

DiagrammeR::create_graph() %>% 
    add_global_graph_attrs("layout", "dot", "graph") %>%
    add_global_graph_attrs("concentrate", "true", "graph") %>%
    add_global_graph_attrs("rankdir", "TB", "graph") %>%
DiagrammeR::add_nodes_from_table(
    table = ndf1,
    label_col = label) %>% 
DiagrammeR::add_edges_from_table(
    table = edf1,
    from_col = from,
    to_col = to,
    from_to_map = id_external) %>% 
    render_graph()

`

But as I add clusters - 2-way arrows between nodes of different clusters turn into 2 one-way arrows:

`ndf1 <-
data.frame(
id = c('a', 'b', 'c', 'd', 'e', 'f'),
label = c('a', 'b', 'c', 'd', 'e', 'f'),
cluster = c('1', '1', '2', '2', '2' , '3')
)

edf1 <-
data.frame(from = c('f', 'c', 'f', 'a', 'd'),
to = c('c', 'f', 'a', 'f', 'e'))

DiagrammeR::create_graph() %>%
add_global_graph_attrs("layout", "dot", "graph") %>%
add_global_graph_attrs("concentrate", "true", "graph") %>%
add_global_graph_attrs("rankdir", "TB", "graph") %>%
DiagrammeR::add_nodes_from_table(table = ndf1,
label_col = label) %>%
DiagrammeR::add_edges_from_table(
table = edf1,
from_col = from,
to_col = to,
from_to_map = id_external
) %>%
render_graph()`

As I checked - inside cluster 2-way arrow works fine. It only breaks between clusters. Looks like no one ever tested concentrate attribute with clusters. Could it be fixed?

`
grViz("
digraph G {

concentrate=true

subgraph cluster1 {
  'c'
  'd' -> 'e'
}

subgraph cluster2 {
  'a' 
  'b'
}

subgraph cluster3 {
  'f' -> 'a'
  'f' -> 'c'
}

 edge[color = black]
                 
'a' -> 'f' 
'e' -> 'd'

}
")
`