StyleInjector

I'm using Smartgwt 4.0 Dev latest nightly build version.
I'm drawing two canvas component with different dimensions. i'm rounding them using CSS. I receive their dimensions, including the radius from DB and because of using CSS in need to inject the radius there. I've suceeded this but it uses the latest injected value for both canvas objects.
I've used:

StyleInjector.inject(".curved_ {border-radius: "+buttonRadius+"px; behavior: url(PIE.htc);}",true);
canvasCircle.setStyleName(".curved_");

This piece is executed for 2 different objects of type Canvas.
Why is this happening?
Thnak you