Slur placement="below" not saved in MusicXML export

In the example music, the last slur was forced below in MuseScore. When exporting as MusicXML, this forced direction is lost.

Here is an example of the forced slur created in MuseScore with the Inspector open:

After exporting to MusicXML and reloading the file, the slur is marked as having an automatic direction:

The MusicXML export (see attached) does not contain a placement="below" attribute on the slur, so the bug occurs when the forced placement is exported into MusicXML.

In contrast, the third slur is forced above, and this is preserved in the MusicXML export and recovered when loading the MusicXML file back into MuseScore:

<slur type="start" placement="above" number="1"/>

The first two slurs are automatically oriented, and they remain the same in the MusicXML file and in the import back into MuseScore.