oha, muss natürlich statt
foreach($_POST["subnavlink"] as $key => $value)
print $key . ": " . implode(", ", $neuesArray[$key]) . "<br />";
so heissen:
foreach($_POST["subnavlink"] as $key => $value)
print $key . ": " . implode(", ", $_POST["subnavlink"][$key]) . "<br />";