Stained Glass Invisible Underwater

When viewing stained glass that is in the water, from above the water, the stained glass is invisible, however, for regular glass, it can still be seen. It makes it very difficult to use stained glass underwater, due to its invisibility when viewed out of the water.

If not a bug, but rather a feature, then why isn't regular glass treated the same, and invisible when viewed above water.

Thanks

Crimson