dot tool doubles arrows - cluster-computing

Question

I've recently been using dot to create flow- and callgraphs of a rather complex assembly program. All in all this works perfectly fine, with just a little hickup. Sometimes, when drawing a line from one node inside a cluster to another node in a different cluster, the line somehow doubles.
I've added a stripped down version of my problem as code and a dot output image.
Thanks
digraph G {
ratio=auto; node[fontsize=12]; label="boot"; newrank=true;
{
node[shape=plaintext];
1->2[arrowsize=0.7,penwidth=0.1];
}
Reset->uart_init[arrowsize=0.7, penwidth=0.1];
{ rank=same; "Reset"; "1"; }
{ rank=same; "uart_init"; "2"; }
/* terminalhooks cluster */
subgraph cluster42 {
fontsize=12;
label="terminalhooks.asm";
labelloc=b;
type->emit[arrowsize=0.7,penwidth=0.1];
emit[label=<emit<BR/><FONT POINT-SIZE="8">Terminal redirection hooks<BR/>für eventuelle Umleitungen</FONT>>];
}
/* stm-terminal cluster */
subgraph cluster43 {
fontsize=12;
label="stm-terminal.asm";
labelloc=b;
emit->serial_emit->serial_qemit[arrowsize=0.7,penwidth=0.1];
serial_emit[label=<serial_emit<BR/><FONT POINT-SIZE="8">Ausgabe Char via UART</FONT>>];
serial_qemit[label=<serial_qemit<BR/><FONT POINT-SIZE="8">Prüft TXE (Transmit Buffer Empty)</FONT>>];
}
{ rank=same; "type"; "emit"; "serial_emit"; "serial_qemit"; }
}
dot graph

Answer 1

I have no idea why this happening, but adding tailport=e seems to fix it:
emit->serial_emit->serial_qemit[tailport=e,arrowsize=0.7,penwidth=0.1];
# -----^-----
Edit:
It appears the newrank atr causing the problem.
digraph G {
newrank=true;
subgraph cluster42 {
0;
1;
0->1;
}
subgraph cluster43 {
2;
3;
1->2->3;
}
{ rank=same; 0; 1; 2; 3; }
}
produce:
but if you remove:
newrank=true;
it produce:
Edit 2:
For this example you can use rankdir=LR and remove the rank=same:
digraph G {
rankdir=LR;
subgraph cluster42 {
0;
1;
0->1;
}
subgraph cluster43 {
2;
3;
1->2->3;
}
}
maybe you can do same with your complex graph too.