offsetX/offsetY/scaleX/scaleY properties of DisplacementEffect are not managed

1) Drop a Button
2) Add a DisplacementEffect
3) Set offsetX=10, offsetY=20, scaleX=2, scaleY=3, wrap=true
4) Save the file
    => in the file offsetX, offsetY, scaleX, scaleY are absent (i.e. they have their default values)
    => wrap has the correct value

I put a breakpoint in metadata layer and noticed that it receives
offsetX=0, offsetY=0, scaleX=1, scaleY=1, wrap=true

So it looks like the DisplacementMap editor is not collecting
values from the textfields.