Rain does not appear in stained glass

I discovered this completely by accident. I had decided to build a house using light gray stained glass for windows for style. I had also created a porch on said house using carpets and barriers and didn't know if rain passed through carpets, so to test I ran "/weather rain". When the test showed that rain does not pass through carpets I went back inside and noticed that the rain did not appear in the stained glass windows.