When adding cullface to the tops of bottoms of glass panes, nothing happens. It is yet to be discovered if this affects any other blocks.
- Create a resourcepack that tries to add cullface to the tops or bottoms of glass panes
- Open the game
- Place a glass pane with a full opaque block above or below
- Go into spectator mode and view the top or bottom of the glass pane from inside that block and notice that they're still there