Not totally sure of what your issue is here but just for fun, make sure you have the light through transparancy switched on in the render room. Otherwise, make sure your tumbler is not "inside" the plastic window object frame. I've had really strange results when an object encompasses another for lighting effects. An example would be putting something inside a light bulb. The stuff inside the light bulb doesn't get the filters and plug-ins applied to it correctly in lots of ways which aren't worth delving into here but it is a pain. Just make sure your plastic window is a flat plane and not some kind of box with your tumbler iside of it. Just stabbing in the dark but see if that helps. -Kix

-Kix