I have a glass part like a window… however when you look through it the objects that are meshes that are in front of it are not visible. This is on high graphics setting too, on pc.
I also know that water terrain is not visible this same way, but i dont understand why mesh parts exhibit the same characteristic.
Parts that are just a bit transparent are also not visible, same with billboard guis, surfaceguis and text in general, im assuming it has something to do with how roblox renders glass material… so its best to use plastic with transparency for windows.
Ahhh i did set the transparency on the mesh a bit, so that must be it… i will try to set it to zero and see how it comes out.
My glass is meant to see through water… its a giant aquarium glass, so I like that it can see through water, just not objects 
update: worked like a charm.