[MusicXML export] bad positionning of dynamics marks and hairpins/wegdes

With Musescore 2.2, the default positionning of dynamics (piano, fortissimo, ...) is under the stave; this is defined in style setup by vertical offset = 8.00esp
For choral scores, the desired positionning of dynamics is above the stave; to obtain this, a model is created with style setup vertical offset = -1.00esp
This positionning is not correctly exported to MusicXML

• Create a model with vertical offset=-1.00esp for dynamics marks
• with this model, place several dynamics marks at default position (relative vertical offset=0.00). The dynamic marks are positionned just above the stave
• export to MusicXML
• close MuseScore
• import the MusicXML file
• all dynamic marks are moved far above the stave

The same problem occurs for wedge/hairpins