Rendered MusicXML files with tracks that have grand staves

[mxAlexG]

Hi,
I noticed that for rendered MusicXML files, the tracks with grand staves have greyed out beats for the bass clef. According to the documentation, this is due to beats being part of a voice that has an index greater than zero.
I only tested for piano tracks using different files from different sources. I would appreciate it if you could pinpoint where in the MusicXML Importer this logic is implemented to quickly focus on resolving this issue.

Example showing this:

Thanks.

UPDATE:
It seems that the source files I used contain the voice value 4 for piano tracks, the ones downloaded from musescore.org. Could this value be added by Musescore MusicXML exporter by default?

[mxAlexG]

[mxAlexG]

<score-partwise>
  <work>
  ...
      <software>MuseScore 2.1.0</software>