[GP] Dots are not displayed in .gpx format

Nightly 421f366/ Windows 7

1) Create a new score for guitar with GP6
2) Enter some notes with dotted note values (all in Voice 1)
3) Export in .gpx format
4) Save -> Load the file with MuseScore. This one: test gp dots.gpx
Result: the dots are not displayed. Corrupted score in appearance with this sheer lack of dots into the score (no warning however)

Works as expected by exporting in .gp5 format, as can be seen here: test gp dots.gp5

- As far as I could go back in time, I see the same issue.
The image below was produced with this Nightly:f031e87 (EDIT: maybe related?)

(Note: the file can not be opened three weeks earlier with this one: 56177c3)