Too many dots on unisons

[axgeertinger]

Not sure whether this qualifies as a feature request or a bug report: Dotted unisons in double stem notation sharing the same notehead should only have one dot, not two (cf. Behind Bars, p. 58). This:

<staff n="2">
    <layer n="1">
        <note dots="1" dur.ppq="6" dur="4" oct="3" pname="a" stem.dir="up"/>
    </layer>
    <layer n="2">
        <note dots="1" dur.ppq="6" dur="4" oct="3" pname="a" stem.dir="down"/>
    </layer>
</staff>

currently produces this: The lower dot should be omitted. The problem only occurs when the notehead is placed on a staff or ledger line, not between lines.