Glass material in viewport doesn't show world objects behind it

I don’t know if this is intended or not, but it didn’t use to happen up until a week or two ago
When setting the transparency of a glass part located inside a viewportframe, instead of the part becoming transparent, it just shows the background of the viewportframe unlike other materials.

This also happens on the actual game, not only in studio
Edit: Repro file just in case Baseplate.rbxl (20.0 KB)

Looks like a bug. Investigatiing.