Status
Fixed
Issue description
I have recently created a new block to my mod which is based on a slab.
The problem appeared when I stacked the slab and it became a full block. Despite having 0 and 255 opacity (I tried both) the full block remained transparent, letting light through. There is a way to use procedures to manually replace the block if a slab is placed on top of another slab, but the feature of creating custom blocks was created to ease the process of creating slabs, stairs, etc. It would help me a lot if you could take a moment to look at it.
This also appears to happen with stairs to, as far as I've checked...
I created a sample workspace and shared a clip for you to check the bug:
If you check your 255 opacity slabs, opacity is set to 0 in fact. Setting it back to 255 might fix this, but the next time you edit it, it will revert back to 0 which is a bug.
The same applies to has transparency checkbox.
I will fix this in 2020.3.