When using regular one-way glass, the rainfall outside could't be seen while it can be seen through normal glass blocks and panes. I don't know if it is a feature or a real bug though. Left two are normal glass, right ones are regular one-way glass. It requires one-way glass made with regular glass and distortic mirror, place it near a placed normal glass block or glass pane, then wait for the weather to change to rainfall or storm. One way glass will not show the outside falling drops, aldo it has this weird upside dark downside lighter effect, like underwater.

I think the render type needs to be changed to cutout for it, but in the meantime, you should be able to use fabulous graphics for it to render correctly.