Take a simlpe dot file, for instance :
$ cat > simple.dot <<EOF
strict digraph "test" {
"titi" -> "toto"
}
EOF
then run dotty :
$ dotty simple.dot
then right click, select "print graph", then "file", then
a filename and any combination of format and orientation.
Then go check your PS file with for instance gv.
GV will display the graph then blank it immediatly.
When printing, the page is blank.
One converted to pdf, xpdf on it behaves like gv on
the postscript (display then erase).
The easy workaround is to use dot with -Tps instead.
Notice that the outputed PS file is completely different from
the one generated from dotty.
I suggest removing the print graph option alltogether from dotty :-)