Did you see this part of Michael Bush's post about his observation hives?
Space between the glass:
For reasons unknown to me, no one seems to get this right. The draper has about 2 1/4" between the glass and the bees burr the glass up a lot. The Brushy Mt. hives have 1 1/2" between the glass and when I put in frames of brood from a hive it was too tight a fit and the brood could not emerge and the bees absconded. I reworked the Brushy Mt. hives by adding a screen molding (available at the hardware store) which is 1/4" thick. I put it behind the hinges on the hinge side and behind the door as a stop on the opposite side and added one next to the door just to match the other side. This has worked perfectly and it is my most thriving hive now. 1 3/4" is just the right amount of space between the glass for an observation hive. 1 7/8" is ok.
Do you think maybe you have too much space between the glass, and that's why they're burring it up? By the way, the awnser to your real question is, no I have no idea what the magical solution is, sorry