I believe the problem  may have something to do with an aritifact stemming from the automatic Index of Refraction settings.  That shader category to me always seemed quite arbitary, and the results, unrealistic.  In your refraction setting, try installing and playing around with one of the value shaders instead.  It may yield better results.

Or you can install one of the plastic shaders and tweak it until you get something like a Plexiglas effect.