I seem to recall the mining laser ignoring glass (and striking the block behind it), but I can't recall if that's a memory of IC2 or IC1. Being stopped by glass doesn't seem right, though. Diffused maybe, refracted, reflected even, but not stopped.
You are right, it used to pass through glass. I remember now back in IC1 starting forest fire several times when I would forget this while using the laser during building remodeling. I think since IC2 I have ony built a couple lasers to play with the different modes.