OK, finally I fix this issue and it was not related to this extension.
I was creating a new Image with a "fromColor" Texture, and then changing the texture for my needs doing : myImage.texture = new Texture(...);
This Image was used as the masked Image.
And in this case, it seems that one of the texture (the first one I suppose) was never disposed...
So if you apply a texture this way...be sure to dispose the first texture before assigning a new one if you don't need it anymore.