masking text3D in papervision3D

I have a text3D and I want to mask it with a Plane . I usually mask my things by defining two ViewportLayers , then开发者_开发知识库 give every object a Layer by
myLayer1 = viewport.getChildLayer(myobject1);

myLayer2 = viewport.getChildLayer(myobject2);

and then mask it by

myLayer1.mask = myLayer2;

and it works , but when I try to mask a text3D object it doesn't work at all!

anyone has any experience with it ?

thanks